For more background, I was able to use both my primary account and the rest of the family’s accounts to access my home hub with the classic app. Using the new app, my primary account would see my home devices under my summer cottage hub (the original Kickstarter v1 hub). The other accounts could see and control the devices in my home and everything worked fine.
When, after the region change of my primary account, I still couldn’t access my home hub with that account, I tried to delete my home location from that account (so that I could re-invite that account using my home locations owner account). Well, my home location was also removed from its owner in the new SmartThings app. The owner could still see the location in the IDE, though. According to the IDE, the owner of the location was my primary account (which couldn’t see the location in the IDE).
Support confirmed that the situation: “It is very odd that it would be claimed to that account after the Location is owned by a different user and has been deleted.” and recommended: " I’ve had checked and there is absolutely no way that we can change the owner of a Location right now, and thus my recommendation would be to factory reset the [my home location] Hub and reset all of the devices connected. I can appreciate that this is not ideal, however, due to the Location being in some kind of limbo I do believe this to be the best route to take."
I run the factory reset procedure to the hub. Currently I can see two instances of it in the IDE:
The IDs of the second and third row are identical, except that the third has the _16…_DELETED attached to it.
I think it’s a pretty ugly situation. It would probably easiest to ditch that hub altogether and just buy a fourth one. I’ve already spent two days trying to reconnect all my devices to my home hub. It seems that some of the cloud-to-cloud integrations are still tied to that _DELETED instance and fail to re-install to the new.