sieve is working/forwarding mail - but not for all users

Hi,

we have dovecot-ee-2.2.18.2 and pigeonhole/managesieve 0.4.8 running for some time.

Today some users informed us that they did not get mails from one project account forwarded to there personal accounts any more.

This worked till one week ago and I cant think of any changes we made...

The project account keeps a copy of received mails.

I tried two different accounts to configure forwarding to internal and external mail addresses which is working.

Question: Any hint or idea? How may I debug sieve forwarding?

Thanks and regards . Götz