I've been having same issues. I'm beginning to think that it has to do with the use of common network name for the 2.4ghz and 5ghz streams. I don't think the Xfinity router can effectively pick/manage the best connection and seamlessly do the hand-off from the 2 streams. I've noticed that when I lose the connection, the signal strength (even though my device is stationary) goes up and down. Once it settles on a stream, connection re-establishes itself and starts working. I did an experiment this morning by conncting an Apple Airport router to the Xfinity router. For the Apple Airport, I only broadcast in 2.4ghz. I have not had a single droppped connection from the Airport, but other devices connected to the Xfinity router that is doing simultaneous 2.4/5 transmission continues to have drops.
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