imap-login: Error: BUG: Authentication server sent unknown id

I randomly get these errors on my Director

Aug 17 10:52:37 imap-login: Error: BUG: Authentication server sent unknown id 98448 Aug 17 10:52:37 imap-login: Warning: Auth connection closed with 2 pending requests (max 2 secs, pid=27036, Received broken input: FAIL 98448 user=user@example.com) Aug 17 10:52:37 auth: Warning: auth client 27036 disconnected with 1 pending requests: EOF

2.3.2.1

-- Tom