Some feedback after trials…
It seems that the issue is coming from Privacy Guard. If it is OFF, every time I switch the phone on, the call history (and the contacts. I did not mention above, but when I experienced the problem with the call history, also it was not possible to see the contacts, since they were not displayed, only a turning wheel going on and on) was there. After a couple of weeks of tests, it is consistently the case, so my conclusion is that Privacy Guard was guilty.
Before switching it off for all the apps, I had tried to selectively switching it off for some apps or some tasks, but I was not able to find the right set up, since the phone behaved in the same way as before (sometimes I could get the call history, without a clue why it was random).
Now, the question: I thought Privacy Guard was a good idea (even though I recall reading some posts where some issues with Privacy Guard). Is it OK to keep it off? Or how to switch it on without affecting the normal working of the phone?
Thank you in advance