iPhone 7 - randomly - screen goes to "lit black" when hitting home or sleep button and won't come on

My iPhone 7 started behaving strangely over the last week. At random occurrences (or so it seems), when I hit the home or sleep/wake buttons to access the phone, instead of turning on with my background picture and the fingerprint login option, my phone screen just goes black. But it is a "lit" black - i.e, the phone screen is active, it's just displaying an all black screen. When I hit the sleep button it turns back off. When I hit it again, it goes back to lit black again.

After several minutes of playing with it, it finally comes up w/ a screen where I can login via fingerprint again. I tried and tried to hard reset the phone and it wouldn't even do that. After I hold down the two buttons (home/sleep) for at least 30 seconds, I give up and release the buttons and it snaps a screen shot.

I tried holding down the volume down and sleep last night, but that made it to wear my screen turned off completely (not lit) for a while.. I had to plug it in, play w/ different button combinations, before I could finally make it reset last night.

But again, my phone is doing it this morning. I'm afraid when/if I took it to the apple store, it would stop behaving like this.. it's random. Anyone ever experience anything like this?