Just as the title says, for no apparent reason, when I'm not touching any of the buttons or sticks on the controller, button prompts just revert back to PC. and there's nothing pressing any keys or mouse moving or anything. Any ideas? doesn't seem like anyone else has had this issue.

I've been having the same thing happen to me.

It has to do with some conflicts in the InputTemplates.txt file. Go to the PC Gaming Wiki and you'll see a section for "Controller mapped incorrectly," you can download a corrected InputTemplates.txt file. It stops that back and forth switching between keyboard and gamepad that you see in-game.