Mine is doing the same thing. If you hold down on the camera app icon, go to app properties, force stop. I find this closes the app and stops the refining without a reboot. It's a pain that it does this now. Seemed to start after the last software update.
Another user susgested this and it worked for me:
"Go to Settings, device care, tap battery, then look for the camrea app, and make sure put to sleep option is turned off."