Try changing the device type/handler to the version 1 of the SmartThings outlet and see if that works. I did that and it worked for me although it might just be coincidence. I then later changed the device type/handler back again.
If that still doesn’t fix it, then you will probably need to go through the process of resetting it. Unplug it and then plug it back in while holding down the On/Off button, wait a couple of seconds and then release the button after you plug it in. Go back into the SmartThings app and try to re-pair it. Sometimes, it won’t even show you if it finds it but a new thing will show up. Hopefully, that is a permanent fix. Don’t remove the original device yet because sometimes, it will start working again after a few hours and the new thing stops working. This has been my experience, FWIW.