I just received my brand new Librem 13, set it up and run into this:

• try to connect to some protected WiFi.
• a password prompt for the WiFi key appears
• wait (while trying to find the correct key.)
• screensaver pops up
• try to unlock it
• it probably does not work because the password prompt still tries to capture all input.

I had to power the laptop hard down by long pressing the power button.
I'm quite new to PureOS, so it might be, that I did not find the correct way to activate the unlock mechanism, but normal screen saver is easy to unlock.