Have 'run into' similar when migrating a copy of a 1.9.16 to a 2.x.
Should have checked all third party (add-ons) in the 1.9.16 for 2.x versions. Fortunately for me, many of the add-ons had a version 2.
Downloaded the version 2 mod/block, installed manually ... unzipped the zip on local machine or work area on server. Moved the resulting folder into proper place in the M2 code (block/mod). Set permissions correctly.
Any 1.9.x add-on for which I could NOT find a version two, I removed from the 1.9.x copy.
Checked the 1.9.x copy for functionality ... broken courses that used the add-ons - and made individual course backups - with labels/notes concerning the add-on's no longer being available. At least the teacher, when logging onto the migrated site, could see info and be informed.
Then went forward with the migration of the 1.9.x copy to 2. It did result in a 'cleaner' migration.
Will it work 100% of the time? Uhhh, wish I could say that. Depends upon the blocks/mod add-ons ... and if the version 2's were compat with the Moodle version to which migrating. Discovered not all version 2 mods/blocks, etc. were compat with all version 2's. :|
But, would also like to hear of experiences of others! So please post your solution.
'spirit of sharing', Ken