Nominet DRS Policy Section 21, page 11 <
https://media.nominet.uk/wp-content/uploads/2017/10/17150434/final-proposed-DRS-policy.pdf> reads:
21. Repeat Complaints
21.1 If a complaint has reached the Decision stage on a previous occasion it may not be reconsidered (but it may be appealed, see paragraph 20) by an Expert. If the Expert finds that a complaint is a resubmission of an earlier complaint that had reached the decision stage, he or she shall reject the complaint without examining it.
21.2 In determining whether a complaint is a resubmission of an earlier complaint, or contains a material difference that justifies a re-hearing the Expert shall consider the following questions:
21.2.1 Are the Complainant, the Respondent and the domain name in issue the same as in the earlier case?
21.2.2 Does the substance of the complaint relate to acts that occurred prior to or subsequent to the close of submissions in the earlier case?
21.2.3 If the substance of the complaint relates to acts that occurred prior to the close of submissions in the earlier case, are there any exceptional grounds for the rehearing or reconsideration, bearing in mind the need to protect the integrity and smooth operation of the DRS;
21.2.4 If the substance of the complaint relates to acts that occurred subsequent to the close of submissions in the earlier decision, acts on which the re-filed complaint is based should not be, in substance, the same as the acts on which the previous complaint was based.
21.3 A non-exhaustive list of examples which may be exceptional enough to justify a re-hearing under paragraph 21.2.3 include:
21.3.1 serious misconduct on the part of the Expert, a Party, witness or lawyer;
21.3.2 false evidence having been offered to the Expert;
21.3.3 the discovery of credible and material evidence which could not have been reasonably foreseen or known for the Complainant to have included it in the evidence in support of the earlier complaint;
21.3.4 a breach of natural justice; and
21.3.5 the avoidance of an unconscionable result.
Unfortunately in the two DRS cases I have cited in this thread, there is no published explanation detailing why rehearings were granted. Both rehearings resulted in summary decisions and the independent experts chose not to publish any substantive details.