I have HWS and it does that when I first turn it on, but no other time. When they updated the software, I also have to turn the receiver on before the TV, otherwise the TV displays "No HDMI Detected". Fun, ain't it.
I've been seeing the black flashes you describe for several months, on my previous Hopper with Sling, and on my new Hopper 3 (I recently upgraded). The flashes for me mostly happen with live TV and only for the first 10 minutes or so after turning the receiver and TV on. Does not happen with on-demand titles and other TV sources. I tried switching HDMI cables with no improvement. I have a 2015 Samsung 75" TV.
I also see this, usually on a Joey3 when bring up the DVR screen or the guide. Very annoying and the family thinks something is broken, of course. I’m guessing some kind of SW problem. I have a Hopper 3.
I get one, not often with my VIP's. When it happens I think the TV has turned off but within a couple of seconds the picture is back. Has happened a handful of times over the last few months. This is on WA not sure about EA.