Phone call interruption

[jftr]

Is this the same issue?

Black screen during conversations (How to clean the proximity sensor)

A few days ago my Fairphone started giving me a black screen during phone conversations. I noticed it also blacks out while having a conversation through Viber. I can’t do anything while ringing or talking, not even hang up. So when I get connected to voicemail my only option is to take out the battery to hang up. If I do get connected to someone I have to ask them to hang up after we finish the conversation, because I can’t. After that, the phone works fine again. Any clues on how to fix this, …