Hey guys, I also had this issue with the black screen and it made me mad. It appeared around 3 months after the upgrade to Android 7. I couldn't do anything during a call and had to wait until caller terminated the call. Anyway, the solution that helped me further was this: during black screen, just press multiple times and very fast the power button and by the time the screen gets lighten up, just hold the phone upright, so the screen won't turn black again. After that, turn off the phone and let it rest for a few minutes. As soon as it cools down, turn it on again and it should work without issues. If you have any heavy or non-responding apps, then a delete would help further.
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