Strange problem with proximity sensor on Nexus 5X

Question

A few days ago I started experiencing a strange problem with my proximity sensor. When I answer a call and put the phone to my ear, the screen goes blank. When the call ends, the screen stays black. This (as I've discovered) happens to quite a few people.

I started checking with aida64 app. When the app starts, it reports proximity sensor value of 5cm. When I cover the sensor, the value goes to 0. Then I uncover the sensor - and the value stays at 0. I switch from aida64 to any other app and back to aida64 - and the value goes back to 5cm. Alternatively, I can switch the screen off, then on again - and the value will go back to 5cm. Basically, it looks like once the value is down to 0, it won't reset for the currently running activity/app - yet it does reset when the activity is deactivated and then reactivated.

I tried booting in safe mode - same results.

Any ideas about trying to solve this?

The phone is Nexus 5X with PureNexus 7.1.2 ROM and Magisk. Come to think of it, it may have started when I updated magisk a few days ago, but maybe not. Any suggestions on rolling magisk back a couple of versions would also be useful.

EDIT: I uninstalled magisk altogether and the problem persists, so it can't be magisk related.

Answer 1

Answering my own question. As I didn't have much to loose, I opened the phone up and found HUGE amounts of dust inside, including around the proximity sensor. The whole sensor was just clogged with dust. I took out all the tiny parts, gaskets, etc., carefully cleaned everything with a soft brush and re-assembled the phone. Voila! Everything works correctly now.

I suspect the dust was getting in the way of the light in the proximity sensor - but it wasn't fully closed due to the dust moving around there.