Why won't my phone buttons work on android pie? (hang up, speakerphone etc.)

I have a OnePlus 6 phone that has android pie. About half the time I go to hang up a phone call or put it on speakerphone, the buttons don't work. They simply don't respond. The only way I've been able to hang up is to swipe down from the top and end the phone call from there. Is this an android pie bug, and is it possible to fix?

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