So much incredible progress with HA, I stand in awe of what the community has developed.
One annoying issue persists for me. Sometimes when a device or entity is deleted it remains in the database but unusable.
We need a way to delete these orphan devices/ entities.
I think there are several WTH posts along these lines. You might do better to vote for one of them.
Or at least for your own. 
Closed as a duplicate. Please search the category before posting. You can vote and comment here: WTH there isn’t a System Cleanup and/or here: WTH missing entity repair items