No responce from oc 9.1.5 after logout


during a web-session of showing my files, I select "logout" from the menue.
This ends in a timeout "no responce..."

A new connection is also running into a timeout.

Changed the loglevel to DEBUG and checking the owncloud.log -> no - new - entries at all to the logfile.

I'm running the owncloud at

PHP. in general, is working. Other WEB-Access to the domain is working.

Any idea what stops working here?