I think the trick lies in disabling.
I originally had your same problem until I did this.
Thanks for your answer.
This only disables all entities related to devices (available or unavailable), but devices are still there.
If the devices are unavailable (and for sure it will never be back in the future), I’m not able to delete them without removing the integration… that’s my concern.
As browser_mod is probably based on a cookie that is related to the session context, the behavior seems correct: when clearing the entire cache, it will delete the ID related to the device and create a new one when the browser reconnects the next time because it is considered as a new device.
But I would like to clean up the mess without having to remove and re-add the integration.
By looking at the community feed I finally found an old thread that cover this problem : Delete individual device (and entity) from integration - #55 by SnoWake
This is apparently not only related to browser_mod.