Eddi, you said you have downgraded to 3.9.2. Is it working fine now or did you have to downgrade to 3.9.1?
3.9.2 had a bug with showing groups with space in the Admin Console (not in the clients though), so if it only breaks with 3.9.3 i wonder maybe a fix had a side effect. If only 3.9.1 helps with the issue (antubis issue seems to be different) then it widens the number of changes which could have introduced this issue.