Can't hang up calls sometimes

This tends to happen when I am on hold or otherwise in a situation where I want to hang up a call I have been on for a while. It also happens if I am on a call and temporarily navigate away from the call screen to check some other app (like if the caller asks if I got their text or something).

The end call button turns green and does not hang up the call when pressed. To put it another way, there is no red hang up call button, just the green button to make a call.

I can hang up by rebooting the phone, but this hasn't prevented the issue from happening again. This is an iphone 12 and the iOS is up to date.