Just to make sure i understand your scenario:
You are connecting to your soundbridge using the range extender -> bt hub -> soundbridge? Are all these devices connecting wirelessly each other?
I guess this is not a problem of portforwarding. I think this comes through temporary timeouts or it is the wpa key refreshing of your wlan devices. Portforwarding makes no sense because you are using it in your LAN not over Internet, right?
I can’t explain this because i am not a pro on networking and never used such things like a range extender but maybe this is an hint.
Greetz
Osik