HomeKit invitation failure / spinning wheel on specific Apple ID's

I am having the same issue as reported in HomeKit invitation failure and am reopening the thread as Apple seems to have closed it down / no updates are possible in the thread.

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I've got homekit working on my devices. I invited my wife - the notification pops up, but when we go into the home app, and homes, what's there is "My Home (Guest)" with a spinning wheel.

On her iPad, it has the correct home name, on her iPhone is has the default name - both as Guest and both with the spinning wheel.

I have tried:

1) Canceling the invitation

2) delete the spinning home

3) Reset her icloud keychain

4) hard device reset

5) restore the device from backup (Apple's typical default troubleshooting step).

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I have had a case open with Apple for almost a year now and this is no closer to resolution than the day I opened it.

To summarize...

- If I / "User 1" send a HomeKit invitation to "User 2" (in this case, one of my kids), the invitation is received, accepted and acknowledge - everything works!

- If I / "User 1"send a HomeKit invitation to "User 3" (in this case, my wife), the invitation is received, accepted but is never acknowledged from a HomeKit perspective on the recipients device.... SPINNING WHEEL FOREVER!!!

The image on the left shows the spinning wheel.

Meaning, I am simply left with the spinning wheel on the recipients device. However, on my / the senders device, it indicates that the invitation is received and accepted.

I have gone through all the troubleshooting with Apple, provided logs and still nothing further. In addition to testing with each new iOS update, still am no closer to resolution. Had this issue since iOS 10.x and currently running 11.2.6 as still the same issue. I do not believe this is iOS related (at least directly). Although an argument could be made it is the integration with iOS and Apple ID's based on my testing (see below).

One additional piece of information I would like to add... If the invitation is sent from "User 2" to me / "User 1", everything works. Now, if "User 2" also sends an invite to "User 3", the invite is send and accepted... HOWEVER, instead of seeing both "User 1" and "User 3" the list of "People", only a single user (typically the user that accepted the invitation last) is listed.

This implies to me there is something within the Apple ID that is causing the issue. It seems that Apple believes that "User 1" and "User 3" (based on my examples) are the same? Which is why you only see one user in the list of "People" that can manage HomeKit devices after invitations are sent / received / accepted.

However, I have gotten no where fast with Apple support. The only response I get is that "Engineering is working on it". Which is frustrating since my case has been open for almost a year, I can replicate the issue on demand and I have provide them with the information above.

Any thoughts / insights would be appreciated.