I'm experiencing a few quirks following migration back to classic projects for the more robust reporting and permissions structures.
Many of these issues have stemmed from the differences in how Nextgen and Classic projects handle Issue & Epic relationships.
Our Classic projects now show the original Nextgen Epics as "Parent" issues while still allowing links to Classic epics at the same time.
This also causes many issues to not display on the backlog as the board thinks they are a subtask issue type? (Guessing at cause there.)
Here's what it looks like on a board:

The Classic epic above is shown in its proper place as an epic badge. MT2-6 is the errant "Parent" epic from the issue's old Nextgen project.
Has anyone found a strategy for cleaning these "Parent" links up?