I used to have two locations and two hubs. Home and Work.
I took my hub off the Work location to lend it to someone. Now I want to add it back. When I go into the IOS app I see my two locations and “Work” has no hub. But I see no way to add the hub back in. How is this done? The IDE says see the mobile app to add a hub but provides no help.
First question, is why do you want to run two hubs?
I think you need to get rid of the old work one from the system first. I am not sure if adding it as a second hub is any different than adding a new location. Here is how to add a location:
One is at home and one is at work, hence the names 
So I have to delete my work location to add the hub back. That seems silly. I’ll have to try that later. Thanks.
Ah I guess I miss understood the question. I thought you were trying to use the second at home as well. I would think that if you plug back in the second hub it should reconnect. However, someone else used it and had it connected to there account, I assume, so your bigger issue may be did they remove it or not. My guess is you will still need to re-add it as new since the device needs to be associated to your account and connected to the ST servers under you.
I guess my wording was not clear. I said I took the hub off my work location. By that I did mean that I deleted it. Now I see no way to add it back.
Before I delete my location does anyone know how to add a hub to an existing location?
SOLVED: I chatted with support and you CAN add a hub to an existing location.
Instructions are midway down the page on this page.
Which currently reads
-Tap the More menu
-Tap the gear icon beside the Location
-Tap Add a Hub (Android) / Connect a Hub Now (iOS)
Note: This option is only available if the Location does not already have a connected Hub
Follow the in-app instructions to connect your Hub