Steps to reproduce
1. did an upgrade from latest 9.0.x version to 9.1 via apt-get update && apt-get upgrade -> no errors
2. run occ upgrade -> no errors
3. disabled maintenance mode
when trying to login via web-page it shows: Access forbidden (Zugriff verboten) CSRF check failed.
windows clients also can not connect to owncloud server
server based on vmware image provided from owncloud and regularly updated/upgraded to latest version.
Operating system: ubuntu