No weblogin from android devices after update

Strangely I cannot login via webbrowser from my mobile phone since the last update.
I see the login screen, type in the logindata. Then I get redirected to a blank page and the URL says the IP Adress with “/?” at the end. If I reload the page it shows the login page again.
My girlfriend got the same issue, also an android device.

Android webview is the newest version, I cleared the cache multiple times, reboot, still not working.

No problems with loggin in from my laptop.

Any help will be appreciated!