I don't know how many devices you have that are 802.11ac capable....
None of which I'm aware (other than my MBP?).
...my cable modem connects to the Airport base station via ethernet and generates a dedicated network for several home automation devices that use only 2.4GHz band or connect through an ethernet Switch. The Plume Wifi also connects to the Airport Base station by ethernet in passthrough mode....
That threw me for a loop until I realized that you must be talking about a 2nd generation "n" Airport Express Base Station which has got two Ethernet ports as opposed to my 1st generation model's one.
In your case the Airport Base station would be configured to run in passthrough mode and just create the second network. So in essence you have one router, the FiOS router, and two systems each generating their own network.
If your Airport base Station is already in passthrough mode then I would check the ethernet cable between it and the FiOS router.
Well, I was about to report that in a predictable reversal of Murphy's Law, the "When you want it to go wrong, it won't" corollary had struck, because I joined my Base Station network to do some experimenting, and it wouldn't cooperate by dropping out.
So I turned my white noise on and got into bed, and just as I
was dropping off, it
began dropping out and woke me up. Aaargh!!!
First, I obviously wasn't as clear about my set up as I thought I was. I'm not using my Base Station in pass-through mode, rather it creates its own network, so I've got two different pairs of networks to work with in the event of trouble.
Under any circumstances, though, your suggestion to swap out the cable is a good one, because even if it's not carrying the network, it is carrying my Internet. (I haven't gotten hold of another cable yet.)
But the bottom line remains that AirPlay certainly has nothing to do with the cable and apparently has nothing to do with the network either, so why do it and my Internet march hand in hand?
This is getting curiouser and curiouser, though, because sometimes the AirPlay dropouts begin almost instantly when I join my Base Station network, and sometimes it's hours before they begin, but my Fios network never experiences any.
Base station failure? (My Base Station is an Apple refurb...didn't test it when I got it...subsequently discovered it won't take a reset.)