I've had the same problem too since the last apple update. I also enabled my guest wifi about the same time, so really not sure which is causing the problem or how to make it work again.
My FIOS app has to be on the same subnet as the STBs to see them.
The Guest WIFI is explicitly set up to not be on the same subnet as the STBs to keep the networks separate.
So you should have the funtionality of seeing some channels and DVR remtoely, but remote control function and full channel list is only available when on the main subnet.