Glad you got it working, Ian!
This is not actually a requirement - we connect multiple hubs all day long in our office without issue. However, some (many?) Android phones have strange Bluetooth “features” that make it more likely to be successful at connecting your Hub the first time if the hub is question is the only one powered up.
I don’t doubt that. There is one Apple manufacturer and hundreds of Android manufacturers. And that leads to many issues between phones.
Can you tell us what Android phones you have tested with that actually preform as expected?
Gary,
The Android operating system has some well-known issues with its Bluetooth Low Energy (BLE) implementation. Performance and reliability varies from device to device as the BLE chips utilized are NOT standardized across all Android devices thus your mileage may vary. This is further compounded with a wide variety of OS running on those hardware platforms. With this in mind it is difficult to recommend a specific model as a device that works perfectly today is potentially an OS upgrade away from underperforming.
Derek
I would add that we do have on our roadmap a task to re-evaluate the BLE implementation in our Android app in an attempt to work-around some of the Androidp-specific issues.
I’m still curious as to what phone you used that worked. And I’m fully aware of the hundreds of bluetooth issues. I have documented a few in reports to Google over that past few years. And I’m aware the every hardware component handles it different and ever phone make handles their firmware differently.
Yes, it’s a big mess
It works well with the Galaxy S8 most of the time but it sometimes seems to get in a weird state when connected to more than one Hub. To be honest, we use iOS devices for most testing and configuration around here!
I have used Samsung Galaxy S6 Sprint, S6 Edge T-Mobile, S7 T-Mobike, S7 Edge T-Mobile, S8 unlocked, S8+ unlocked, Note 8 unlocked and S9+ T-Mobile…
None of the above work reliable with the Hub. And I’m not blaming the Hub. It’s the non-standard standards that are at fault and Google needs to step up and take control.
one of the things you also get with Android based phones, the layers of the provider and/or brand
Long ago I was a tester for some app on iPhone and Android. They were nice to offer me an Android. Since this app was using many parts of the phone like GPS etc it was fairly complex. We were like 12 testers and we all finished by hacking the android phone and go back to stock Android, leaving out all other layers and in almost all cases most problems disappeared. Often those layers bring loads of heavy useless junk (Samsung is the king) and also plain conflicts (one of the providers in France assured any Android crashed once a week even when lying on a desk doing nothing, memory leaks)
Basically Android has the same major problems as windows, all kinda hardware, all kinda software … make a mix and you need to write as many patches …
Not sure Google is willing/able to patch all the breaches of the layers on top 
Android is a mess but I still prefer the OS to Apple.
And with Android you get the basic OS covered by bloat from the manufacturer covered by bloat from the carrier. It’s an accident that any Android actually works.
Maybe that is what I experience once in a while where turning off Bluetooth makes things work sometimes. Maybe a Bluetooth enable/disable at the app level might be useful. I’d have it off most of the time.