*439On February 7, 2015, Bridgewater resident Robert H. Olson died without leaving any known will. He had no surviving parents, spouse, or children. The plaintiff, Dorothy A. Leighton, a first cousin to Olson on his father's side, stepped forward to claim his estate on behalf of herself and two similarly situated relatives. During the resulting intestacy proceedings, in which Leighton was appointed personal representative of the estate, the defendant, Bengt Hallstrom presented himself as a first cousin on Olson's mother's side and sought a proportionate share. However, the Probate and Family Court judge ultimately concluded that Hallstrom's efforts were tardy. Ruling that Hallstrom's claim was precluded as a matter of law, the judge struck Hallstrom's objection *440to Leighton's petition for order of complete settlement. A magistrate then entered a final decree settling Olson's estate without Hallstrom receiving any share. Because we agree with Hallstrom that the judge erred in various respects, we vacate the order *97allowing Leighton's motion to strike and the final decree settling the estate, and remand for further proceedings.
Background.2 1. Leighton's petition. Leighton initiated these proceedings on April 29, 2015, by filing a petition for formal adjudication of intestacy. See G. L. c. 190B, § 3-402. That petition also requested that Leighton be appointed the personal representative3 of Olson's estate.4 Leighton's petition listed herself and two other first cousins as "all known heirs on [Olson's] predeceased father's side." It further stated: "It is unknown if any heirs exist on [Olson's] predeceased mother's side and, if so, the degree of kindred and location of such heirs." By checking a box on the court's preprinted form, Leighton requested that the court "[f]ormally determine [Olson] died without a [w]ill and determine heirs."
2. Hallstrom comes forward. By order dated July 6, 2015, a guardian ad litem (GAL) was appointed to represent Olson's unascertained heirs with respect to Leighton's pending petition. Before the GAL filed his report, Hallstrom, a resident of Uddevalla, Sweden, stepped forward and identified himself to Leighton as an interested person. Specifically, Hallstrom's counsel sent Leighton's counsel a letter that included a genealogical chart purporting to show that Hallstrom was the son of Olson's mother's brother (and hence, a first cousin). Using a preprinted form, Hallstrom filed a notice of appearance, which was docketed by the court. On that form, Hallstrom checked the box that signified that his appearance "is NOT an objection."5 His counsel explained in a contemporaneous *441letter to Leighton's counsel, "I have not listed it as an objection since it is my understanding by [sic ] doing so will cause a contest in this matter."
3. The GAL's report. After having discussed the matter with both Leighton and Hallstrom, and after having reviewed the docket and certain other relevant documents, the GAL issued his report, which was docketed on July 24, 2015. That report confirmed that Olson had died intestate and urged that a personal representative be appointed "to take control of [Olson's] real estate and prevent waste as well as marshaling all assets of personal property." The GAL assented to that appointment after noting that Hallstrom -- the only additional claimant who had surfaced -- had not objected. With respect to the key issue of determining heirs, the GAL suggested deferring that issue to the future, stating, "The issue of determining heirs can be addressed during the course of handling the estate."
4. The July 2015 decree. On July 27, 2015 -- that is, three days after the GAL report was docketed -- a magistrate acted on Leighton's pending petition by issuing what is styled as a "decree and order on *98petition for formal adjudication." That decree (the July 2015 decree) was issued on another preprinted form. Through the magistrate's checking the appropriate boxes, the July 2015 decree ruled that Olson had died intestate, and it appointed Leighton as personal representative of his estate. With respect to the identity of Olson's heirs, the magistrate left blank the spaces provided on the form for listing individual heirs and instead checked the box that indicated that the heirs were "as stated in the [p]etition."
5. Post-July 2015 proceedings. In November of 2015, Leighton filed a separate petition seeking court approval to sell Olson's real estate. That petition specifically listed Hallstrom as a purported heir who would be due a one-quarter share of the estate "pending verification of lineage." It also included a footnote underscoring that Leighton was not conceding that Hallstrom was a first cousin but instead still was awaiting proof of that. Leighton simultaneously sent a letter to Hallstrom's counsel seeking his assent to the sale of the property. She explained: "Since [Hallstrom] is a purported heir of the Estate, we are requesting his signature on the enclosed Petition for Sale of Real Estate to expedite the process of obtaining a License to Sell." The letter made it clear that Leighton was not accepting the proof that Hallstrom had supplied to date: "Please be advised that unless and until your client furnishes *442acceptable proof of lineage to this office, the Estate will not recognize Bengt Hallstrom as an heir of the Estate of Robert H. Olson." Hallstrom's counsel responded by providing Leighton the requested assent, as well as by sending her various genealogical charts purporting to document Hallstrom's status as a first cousin. His letter closed by stating, "I trust that this documentation will establish my client as an heir. Please let me know if you have any questions or need any further documentation."
By letter dated March 4, 2016, Leighton informed Hallstrom that she still did not intend to recognize him as an heir because she found his proof insufficient. That letter also included language that could be taken to suggest, for the first time, that the court already had determined that the heirs were limited to the three first cousins on Olson's father's side.6 At the same time, the letter continued to indicate that Leighton would recognize Hallstrom as an heir if "the Court makes a formal determination of [his] status as an actual heir of the Estate." Finally, even though nothing in the record suggests that Leighton ever had taken any affirmative steps of her own to track down whether there were heirs on Olson's mother's side, her March 2016 letter suggested that the onus was on Hallstrom *99"to seek relief in the Probate Court in any way you deem appropriate."
By letter dated May 18, 2016, Hallstrom sent Leighton an additional packet of genealogical records purporting to document *443his status as a first cousin.7 His letter closed by stating: "I believe this is the requested information to hopefully establish conclusively [Hallstrom's] status as an heir, but if there is any further information or verification that is necessary, please let me know."8
In September of 2016, Hallstrom wrote to Leighton requesting an update. It is not clear if any direct response was provided. In any event, some two months later, in early December, Leighton filed a petition for order of complete settlement that sought approval to wind up the estate by distributing it in three equal shares to her and the other two first cousins on Olson's father's side. Hallstrom docketed an objection on January 30, 2017, and followed up about one month later by submitting documentation purporting to show that he too was a first cousin. That documentation included an executed "affidavit of research" from a London-based genealogist, together with certified birth, baptism, death, and marriage records from the Swedish region of Värmland, and the cities of Uppsala and Gothenburg. Leighton moved to strike Hallstrom's objection, arguing that the July 2015 decree already had determined that the heirs did not include Hallstrom and that therefore, on various procedural and jurisdictional grounds, it now was too late for Hallstrom to pursue his claim.9
6. The judge's rulings. The judge agreed with several of Leighton's arguments.10 Relying on language from the Massachusetts Uniform Probate Code (MUPC), the judge reasoned that the July 2015 decree issued by the magistrate must be deemed "final"
*444unless Hallstrom timely filed either an appeal of that decree or a motion to vacate it (neither of which he did). See G. L. c. 190B, § 3-412. He went on to point out that even if Hallstrom had filed a timely motion to vacate the July 2015 decree, Hallstrom could not have met the other statutory criteria necessary to allow such a motion to be granted.
Hallstrom separately argued that Leighton violated fiduciary responsibilities that she owed to him "by failing to thoroughly investigate the possibility that he was an [h]eir." The judge rejected that argument based principally on the timing of Leighton's appointment as personal representative. According to him, Leighton had no fiduciary duties to Hallstrom until she was appointed pursuant to the *100July 2015 decree. See G. L. c. 190B, § 3-701 ("The duties and powers of a personal representative commence upon appointment"). Because the judge viewed the July 2015 decree as simultaneously appointing Leighton as personal representative and determining the heirs, the judge reasoned that "at the time her fiduciary duties commenced, the Court's determination of [h]eirs had already become final."11
Having concluded that Hallstrom's claim to be an heir was precluded as a matter of law, the judge allowed Leighton's motion to strike Hallstrom's objection to her petition for a complete settlement of the estate. A final decree then issued, settling the estate in the manner Leighton had requested.
Discussion. As the judge well explained in his memorandum of decision, the MUPC contains strict procedural constraints to which practitioners must pay careful attention. As relevant here, once an order has issued that constitutes a formal determination of the heirs of an intestate estate, then unless that order has been appealed from or been the subject of a timely motion to vacate, the order "is final as to all persons with respect to all issues concerning the decedent's estate that the court considered or might have considered incident to its rendition relevant ... to the determination of heirs." G. L. c. 190B, § 3-412. Moreover, under the statute, a motion to vacate a formal determination of heirs can be brought in only limited circumstances that would not have applied here. See id.12 Finally, a motion to vacate must be brought *445within certain deadlines, including in any event by "[t]welve months after the entry of the order sought to be vacated." G. L. c. 190B, § 3-412 (3) (iii). Practitioners ignore such procedural land mines at their peril.
However, the key question before us is not whether the July 2015 decree became final (the issue on which the judge focused), but what that decree means. As noted, the July 2015 decree did not purport to set forth an exclusive listing of heirs; it simply included a checked box indicating that the heirs would be "as stated in [Leighton's] [p]etition." That petition forthrightly had acknowledged that there could be heirs on Olson's mother's side; it was just "unknown" to Leighton whether heirs existed "and, if so, the degree of kindred and location of such heirs." Further, by the time Leighton's petition was considered, Hallstrom had already come forward as a claimant and Leighton understood him as such. Moreover, the GAL that had been appointed to represent unidentified heirs also recognized that Hallstrom was a claimant (despite Hallstrom's not having filed a formal objection),13 and *101reported this to the court. In the GAL's view, the identity of the *446heirs would be resolved at a later point in the proceedings. In these specific circumstances, we do not interpret the magistrate's having checked the box on the preprinted form that the heirs would be "as stated in the [p]etition" as constituting a formal determination that the heirs would include only the three individuals specifically referenced in the petition, and not Hallstrom. Rather, Hallstrom's kinship status was left unresolved by the July 2015 decree and never has been adjudicated. Accordingly, Hallstrom was not precluded from raising it in opposition to Leighton's petition for a final settlement of the estate.14 Cf. Day v. Kerkorian, 61 Mass. App. Ct. 804, 809, 814 N.E.2d 745 (2004), quoting Kirker v. Board of Appeals of Raynham, 33 Mass. App. Ct. 111, 113, 596 N.E.2d 398 (1992) ("Issue preclusion is not available where there is 'ambiguity concerning the issues, the basis of decision, and what was deliberately left open by the judge' ").15
One additional observation bears noting. Because we rule in Hallstrom's favor based on the meaning of the July 2015 decree, we need not resolve his alternative contention that Leighton violated fiduciary duties that she owed to him. Nevertheless, we note our disagreement with the judge's assessment that any such *447fiduciary duties were so evanescent as to vanish as soon as *102they were created. After the July 2015 decree was entered -- and despite her obvious conflict of interest -- Leighton continued to hold herself out as the frontline adjudicator of whether Hallstrom's proof of kinship was sufficient. Whatever else can be said about the extent of Leighton's fiduciary responsibilities to Hallstrom at that point, she had a duty not to mislead him about how his claim was to be resolved. Moreover, even though Hallstrom may carry the burden at trial of proving that he is entitled to a share of Olson's estate, see Hopkins v. Hopkins, 287 Mass. 542, 544, 192 N.E. 145 (1934), this does not absolve Leighton of seeing that a fair process is utilized to identify heirs.16 See Doe v. Roe, 19 Mass. App. Ct. 270, 272-273, 473 N.E.2d 719 (1985), quoting DeSautels,petitioner, 1 Mass. App. Ct. 787, 791, 307 N.E.2d 576 (1974) ("it is a 'basic responsibility of the probate judge and of the administrator' to identify a decedent's heirs and assure that his estate is properly distributed among them").17
Conclusion. Because Hallstrom's status as an heir has never been adjudicated, we vacate the order allowing Leighton's motion to strike Hallstrom's objection to Leighton's petition for order of complete settlement and the final decree settling the estate. We remand this case to the Probate and Family Court for further proceedings consistent with this opinion.
So ordered.