If you try to rollback non-vanilla spawners (like creeper, iron golem etc anything you can't get vanilla), they turn to pigs. A fix was given for a 1.8 version but could it possibly be added for all versions?

Was already added in v20: https://www.spigotmc.org/resources/coreprotect.8631/update?update=413581

If experiencing a specific issue, please provide exact steps to replicate.

Please note that changes only apply to data logged after upgrading to a new version.