As a placeholder I will add the following links to other OH community topics.
How to implement Thing upgrades
Possible solution posted by Rich Koshak to recreate Thing
But the first one might be the most relevant due to ebus binding not resolving the message. So it might have to do with either a problem in the OH5 json database during upgrade (hence recreating the Thing), or something in the binding might use some improvement (but just a wild guess).