sometime mine oso will like that, when that happen i just wipe the proximity sensor (top right corner) and the screen will come back.
think is the dirt that cause the proximity sensor to sense something and didnt turn back on the screen.
where is the sensor? Is it because i am using a privacy filter / casing blocking it thus this happening?
Check to see if your proximity sensor is working properly. Go to your dialer and enter *#*#7378423#*#*. Then go to Service tests and Proximity Switch.
If it's working, then it's some software / setting issue.
I did that and it showed On.

