We have tried loading AC 12 and AC migration 11 in different configurations. In the beginning, our default was simply placing the ArchiCAD 11 Migration Library in the ArchiCad 12 folder and selecting it separately in the Library manager, so as a result we had the AC12, ArchiCAD 11 Migration Library, and 3 other libraries (that include CADimage and a couple project specific libraries). That was the first configuration and the one where we first realized that we had a problem.
From there, I experimented with several locations with them all bearing the same result.
By the way, you can see in our screenshot that we placed a folder of "Object Library 9 and 10" objects (older migrations files) in the main "ArchiCAD Library 12" folder. Through using the AC 11, this had always worked for us, so we assume that placing the ArchiCAD 11 Migration Library into a similar location might be the solution. But it was not.
I wanted to add another screen and show the library manager. I will send another post.