I had the same problem and asked Plesk's support.
There was no cloning process running but a stale configuration in the database. After making a backup of the DB they solved the problem with:
# plesk db "delete from misc where param like '%clonin%';"
Regards
In 18.0.57 I still cannot see DKIM information. The error when listing domains seems to be related to "Service provider" view. Switching to "Power user" works.