NI Reaktor plugin crashes MainStage

I don't know enough about crash reports to comment other than to note that your System Integrity Protection is disabled; I doubt that is the cause, but unless there is a good reason for disabling it, it should be enabled. I'd check the SIP status in the other machine you mention.

Setting aside the SIP, the common factor appears to be the concert itself which may have been corrupted somehow. Have you a backup of it that you could try (preferably from a time when you know the concert was working)?

Do you have a backup?

If not, make a backup. Select it in Finder, Right or Control click, select "Show Package Contents". In there, there should be a .Patch file, do the same to that. It should then show each separate component of the Concert including each patch. You could try by process of elimination deleting each patch in turn to see if one of them being absent sorts the crashing. If that's the case, you could then remake that one. Otherwise, sounds like you are into a total rebuilt of it.