Pls share flows and screenshot of the devices to prove something is wrong.
Untill now it only have been vague report and most of the time ended up in users admitting they had done it self wrong and forgot what they had done.
I think it’s best is to forget about the why, because like Geurt said, it’s often a user caused issue. I’d just try to fix this issue using some tools:
Find out in which flows that device actually is used, with use of this flow card:
wait for it to index everything (30 minutes or so)
now remove that particular device
then, Flow Checker will report what flows your device was in, because those flows got “broken” (if nothing gets reported, go to app config, to view the flow errors found)
add that device to Homey again; now, to Homey it will be a brand new device, which cannot be turned on/off by a flow by ghosts
repair the reported broken flows by replacing the ‘old’ device cards with the ‘new’ device cards