Ok, so, I reinstalled librerator. And now my kindle is again acting strange.
I followed the instruction for k4nt here: https://www.mobileread.com/forums/sho...d.php?t=198742
I opened a pdf, set the bbox, read some text. Then I used "Exit Librerator" from the menu to exit the programm, but it keeps showing me the File Chooser Menu. That's the current situation. (last time, I used the home button, it showed me an error message, something about a delay of 5 sec, and then my kindle was bricked)
So, I'm waiting for instruction to exit librerator.
Edit: I have a full root access over wifi, if you need some logs without modifying the current situation.