Sounds similar to issues I was having with HomeKit and my setup.
Specifically I suggest making a backup of your homekit.json when it is in a good working state. Then if you get this problem again, replace the json file from backup and restart.
So far since I posted (link below) this originally (on Jul 13, 2021) I have not had another issue with Unresponsive Items. (so like almost 60 days ago).
