From what I can tell, it's pretty clear to me that it's an Azem shard, however, if it rejoined us or not, it was made ambiguous on purpose. That memoria vision would be the first of its kind, like the crystal wasn't broken or anything and it activated just like that when we got there. If memorias can do this just like that, then.. what's the point of sealing them in the first place? They aren't sealed!

That way, in the future, you can handwave it through a flashback (it was at this time you two rejoined..!!) , or make it an important plot point for later (so durante found the crystal that disappeared.. omg it's shining!)

The fact that Real Golbez was not voiced is a clear giveaway, imo.


I'm still getting the idea it was written this way on purpose, though.