I have a GE switch that has been coming on by itself periodically. I’ve tried repairing but that didn’t resolve it. So today I removed it and re-added it. But when I re-added it, I noticed I now have two switches. I’ve tried every method of removing them (exclusion mode, etc) but the “thing” tile keeps re-appearing (and fails to control the switch). If I force delete it, it will return almost immediately. I’ve rebooted the hub, pulled the air gap out, etc. and still the old “thing” won’t go away.
Check with support@smartthings.com they should be able to remove the ghost device.
Same thing happened to me with a contact sensor. I was able to locate the device here https://graph.api.smartthings.com and delete it. This finally removed it.