In the final version of TRoS, the legacy saber works normally, but there’s a leather band around it now, which implies that Rey did indeed repair it somehow, between the events of TLJ and TRoS. If I were Abrams, I woulda at least made the blade “wavy” or something, to remind audiences of the fact that the crystal got split in half (even if she did repair it, somehow).
Correct me if I’m wrong, but there is a fan edit of TROS that edited the saber’s blade to be instable like Kylo’s, right?