I have two homes as well but don't use a Smartthings hub.
I have two dots at one home and just one at the other.
Where I have two dots one was setup initially where the single dot is (using one account) so it sees and controls devices in both places.
The other dot (different account) only sees/controls devices at that location (it was never setup at the other house).
If both accounts and hubs were initially setup in one house then moved to the second house that would account for Alexa seeing both hubs but only connecting to one.
Amazon remembers IPs associated with each device so you may need to forget the device then reconfigure from the house you intend to use it in.
I'm guessing here but you may also need to do that for the hub