iPhone 8 Sleep/Wake Button Not Working

Hello,

I bought the iPhone 8 when it first came out and have had it since. Recently my phone has started doing this thing where I cannot turn it off. The power button will turn the phone on, take screenshots, and shut the phone down... but will not put it into sleep mode. My volume down button has also been acting up as well. I’ve tried shutting the phone down and when I do it solves the problem for a bit, but always goes back to acting up. I have even tried turning the phone off using AssitiveTouch, but it still will not turn off. Seems to be a super weird software issue. Anyone have any ideas???