I don’t believe the external files would cause a migration failure, as the data migration does not really touch the schema of the file or run any scripts. It should simply be moving data between the two files. I also wouldn’t expect those Perform Script in File to cause a DDR to fail.
Thanks for the input. I’m starting to think the issue is related to indexing. When I ran the migration without re-evaluating indexes and calculations, it succeeded, but when I tried with indexing, it failed.
The migration process is running into some problem while updating the indexes or recalculating fields.