Why is my screen timing out after 30 seconds during a call, but not with other use?

[Android Central Question]

I set my screen to time out after 2 minutes. This is working fine, with the exception of a regular phone call. Ever since I upgraded to OREO on my Galaxy S7, when I have to hit menu buttons during a call (for example), I have to keep turning the screen back on because it' times out after about 30 seconds. I tried smart stay, it doesn't work. It's very annoying. Before OERO, I had no issues. Does anyone have a solution?
Thanks.

 

[B. Diddy]

Welcome to Android Central! Is this when you're on speakerphone, or holding it up to your ear? The screen should normally black out when you hold it up to your ear, since the proximity sensor is active. Or are you saying that after 30 seconds, the screen doesn't reappear after you take the phone away from your ear?