dsync-local(customer@example.com): Error: BUG: Mailbox renaming algorithm got into a potentially infinite loop, aborting
dsync-local(customer@example.com): Error: Mailbox INBOX.Foldername sync: mailbox_rename failed: Invalid mailbox name 'Foldername-temp-1': Missing namespace prefix 'INBOX.'

As for fixing, you could see if deleting dovecot.mailbox.log from both replicas happens to fix this.

Unfortunatley deleting dovecot.mailbox.log on both replicas did not fix the problem.