The white coax from the ONT goes to a splitter in the junction box. One output goes back under the house to the extender, the other goes up to the attic where a coupler connects to the white coax. That coax goes to the input side of a splitter. one output goes to the G1100, the other to a STB. Both splitters are Verizon logoed MoCA 2.0 installed by Verizon as was the white coax.
I mean an RF meter to check the signal levels. Would be to expensive for a one time use. I would just start replacing coax since we already know the extents works with the splitters.
There needs to be good coax from the outside splitter to the attic splitter and from attic splitter to the router.
Talked to Verizon support. Finally got through to a person after many calls over months. They diagnosed the problem as a bad coax. Said I could pay $99 to run new coax or sign up for in-house wiring maintenance, $30 per month and cancellable. No brainer there. Tech arrived today. Immediately said bad extender after looking at lights and not seeing on the network with his test equipment. Swapped out WCB3000N for WCB6200Q. Problem fixed. Since it was a Verizon purchased 3000N, no charge. Even after 5 years! I was about to spend another $40 on cable and connectors with the hope it fixed the problem.
Thank you for all the input. Learned alot.