Until the day before yesterday I used my unlighted cover without any problem. Then Kindle started to froze. I didn't want to throw it away since I really satisfied with it. Then I started to think about a solution to this problem. And today I made a small operation on Kindle as described on the photo. I hope this solves the problem entirely.
Just before writing this thread I found an
old thread which also suggests a solution which is a bit ambiguous. I think that my solution is more accurate If you decided to not use the lighted cover. (Of course you can change to its default with a little effort)
However it will take time to be sure that my little operation is really a solution.
Edit: Using more than 40 days, I can say that it works perfectly