With state succession comes a need for judicial re-organisation, as well as a series of practical considerations for the recognition and enforcement of judgments et al issued by authorities of the various States involved in the territorial dispute. The Crimea is a case in point. Anna Tkachova and Andriy Pozhidayev give a great overview first of the reorganisation of the courts, subsequently of the coinciding complication in recognition and enforcement of courts and tribunals in the respective parts of the country. A very good insight into both parts of the exercise: the formal, law-making part as well as the practical considerations for litigating parties.
Of note is that recognition and enforcement of decisions etc. by Ukrainian courts etc. in the Crimea, and of Russian courts etc. in the Crimea, are not covered by European conflict of laws (as indeed is the case for any third country judgments). Neither as far as I am aware are they covered by any of the export controls /sanctions issued by the EU either. (In contrast e.g. with import of goods from the disputed territories, covered by Regulation 692/2014 and corrigenda viz certificates of origin (linked to the EU-Ukraine association agreement, currently being ratified by the various Member States)).