Problem:
During backup, log messages state that a "copy-only" backup was created instead of a "full backup".
Cause:
Microsoft only supports copy-only backups on secondary replicas.
Solution:
This is usually not an issue as the content of both backup types is identical. However, if you want to use the backup as a base for transaction log backups outside of Protector, you need to ensure the backup is created on the primary replica instead. (See About Microsoft SQL Server Policy Classifications for more details)