Customer is using in his logic a"dummy" attribute. Since the upgrade from 2.0 to 3.0.1 a"migrate" fails. The reason for failure is that the engine makes a query to retrieve the dummy attribute, doesn't find it in the schema and aborts the process.
From the export of the driver, the attribute is indeed configured to "optimize", which is most likely the cause of the query being sent. This is a"notify" attribute, so why would it try to optimize it (it will be discarded anyway).
It is the merge authority setting for the attribute that is causing the query to be issued. The way merge authority is handle was changed between IDM2 and IDM3 to allow notify attributes to participate in the merge if the merge authority was set to to app or eDir.