Thanks for the answer. You are absolutely right. Appdata became utterly confused. Applications stopped working. Need to clean up the backup pool and figure out how to properly set upp the FS to allow snapshots without this interference.
FCP gives me the following warning
This is the result of me running syncoid from my main pool to a backup pool. It might be because I am new at ZFS and are doing something I shouldn't or it is an expected result and I can happily press Ignore warning.
Any input would be greatly appreciated. Thank you!