Yes, that seems to be a bug affecting some phones.
Solution: Please follow the official troubleshooting tool .
archived text Besides a badly calibrated sensor the next most common reason for this issue is dust between the proximity sensor and the screen. For more info check <a href="https://forum.fairphone.com/t/fp2-screen-cant-be-reactivated-during-after-calls-see-first-post-for-workarounds/11874/148?u=paulakreuzer">this post</a>.
Cleaning tips:
Clean the screen of your phone, especially the part where the proximity sensor…
or here:https://fairphone.zendesk.com/hc/en-us/articles/208661706-Screen-stays-black-after-a-call-problem-with-proximity-sensor-