Oh wow, I wouldn't have expected it to carry across so many apps. In a way that might be good though and the fact that it is happening only to you and on two different devices at the same time means there's something these two devices have in common. The apps that you've named all seem pretty mainstream, nothing odd or unusual and affecting some big hitters... I've notice you mention various launchers in other threads. Are you using the same launcher on both devices? I know some launchers can have different features and options. I might try going stock to test if the issue goes away if you're using the same on both.
Speaking of the same on both, is there any chance that since the Samsung was last to have the issue that you recently added an app to it that is also on the Pixel? Any chance that you made a settings change you've been using on the Pixel on the Samsung? Shared similarities keep popping in my head because the devices are different the buds are different but the issue is the same...? Even the OS is different, which almost screams, this is an app. Besides Smart Things do you have any app that does anything with headphone controls, BT connections? Those would be the most obvious but there's also a chance it's something obscure. I don't know why but Phone permission just popped in my head. The phone is working I know, but there's no Media or Headphone permissions but what if something is seeing your call and locking other audio out? Maybe it thinks you're still on the call and refuses to play any other audio because it isn't recognizing that the call has ended. Actually I saw something like this way back, everything feels like Éclair but I'm pretty sure it wasn't that far back. Essentially a call was taken through wired headphones and ended with the button on the dongle but the device would not register that the call had ended. The next time this happens instead of repairing the ear buds try force stopping the Phone app. If force stopping the phone app releases the audio it is either a Phone permission or the Dialer/Phone app itself.