The problem occurs not every time, I have the feeling that letting the lid closed longer leads to the problem happen with higher probability.
So basically, when I do not lock the screen or log out, but just close the notebook lid and wait some time (this is not happening when I immediately open the lid again), when I then open the lid again there is no option to enter my credentials again. Meaning there I don't see the screen you see when you lock your notebook or log in. The only thing I see is the wallpaper (I'm not sure if it is the wallpaper of the log in screen or the wallpaper of the running system since they are the same right now).
I can log in via terminal, but I do not get the option for graphical log in.
I'm not completely sure when this started to happen, but it feels like the 42.2 upgrade (from 42.1) might have caused this.

Any ideas how to proceed? Or fix the problem? Please let me know if you need any information. However, since I'm rather a newbie, you might need to explain how I can obtain all the information you need.

Thanks!