There are many entries like below could be seen every 5 minutes in Instance Manager log
P50030: Cannot remove backup schedule ... - it is assigned to at least one VE (Request failed)
The corresponding OA PACI service template has the mentioned backup schedule resource type.
This behavior is recognized as software issue CCU-19686 by CloudBlue R&D team. Please contact PTA or your TAM in order to check the status of the request or to discuss the workaround.