After a call the screen is black

I searched for any solve but I didn’t found anything. The screen i black and I can’t do anything. I tried to just leave it for a few minutes and sometimes it worked after that, but oftens not. I had to put out the battery and start again. I only get the problem after a phone call, doesn’t matter if I made the call or if I recive a call. Now I recall that this was a problem before, when I had an FP2 or Fp3. It was the promixity sensor. But I can’t find it on FP4. I’ve only got my FP4 a few weeks and I’ve read that other had similar problems but not after calling.

I remember I had this during a call. And when it ended, the phone remained black. Proximity sensor is likely to play a role in this, but I’m not sure it’s of any help to know that. I think I managed to reboot the phone by a long press of the power button.