CP Session expires after short time Our Craft installation is now working on the Production Cloud-Server, except that if I'm logged in the CP, after maybe 30 sec the login-modal pops up and says that the session has expired.
If I just reload the CP, I'm in again without the need to login.

That behaviour didn't show up on the development server.
I didn't make any Configuration Settings like userSessionDuration or something like that, that's all default.

Any idea?
99% of the time when you see this behavior, it's because wherever your server is configured to save PHP's session files to either doesn't exist or isn't writable by PHP.

You can check where that path is by going to yourdomain.com/admin/utils/phpinfo and searching for session.save_path.

If you have the overridePhpSessionLocation config setting set to true, then Craft will set that path to craft/storage/runtime/cache.