After upgrading from kubuntu 15.10 to 16.04, the login screen hangs right after typing the (correct) password and pressing enter. The controls like the text field are disabled and brightness slightly dimmed, then nothing else happens.
By switching to a text console with Ctrl+Alt+F1 and back to X with Ctrl+Alt+F7 I can get into the logged in session, so it seems the screen is just not being updated during login where normally the progress bar is shown.
This doesn't happen always, but most of the time.
It is running on a Lenovo L420 with Intel integrated graphics. Running in VirtualBox on another PC, this does not happen.
Is this a known issue or bug? I wasn't able to find any posts or reports about it.