You are correct, the app shows 8.0 at first then after blocking the sensor it goes to zero. 100 o/o confirmed.
I had done some research online and dirt was one of the theories.
I'll bet its lint, I have it in my pocket most of the time.
Edit ======== Edit
I just blew into my speaker grill and presto, it's working fine. Tested with MyDroid app and it reads 8.0 before and after waving my hand over sensor, it goes from 8.0 to 0 back to 8.0,for now I'm good. I love taking stuff apart so I may make it a mod project, take it apart and seal the opening that allows dust to get
into the sensor area.
sent from my P5113 using TouchPal mind control keyboard. (Beta)
There is a seal in there already, but its not very good. (Obviously)
Sent from your phone. You should be more careful where you leave that thing.