Im on lineageos and also had this problem. To solve this, I open up the phone and clean the sensor. Now it is solved. Happened to me twice and both time it works. You might try this. I don’t know why exactly. 
Im on lineageos and also had this problem. To solve this, I open up the phone and clean the sensor. Now it is solved. Happened to me twice and both time it works. You might try this. I don’t know why exactly.