G3100 router disconnects from ONT

[Saint_Christopher]

A question and problem for the hive mind:

I have Verizon Fios fiber optic internet. It terminates at the ONT (optical network terminal) mounted on my house. From there, coaxial cable runs to the wireless/Ethernet router. My old ActionTec 2.4ghz router (and it’s 2.4ghz/5ghz dual extender that back feeds over coax) work fine. I recently bought the latest Verizon G3100 dualband router and it’s G3200 extender. They worked for about 10 days. This morning, the G3100 keeps dropping the handshake with the ONT. I’ve checked settings, connections, and rebooted everything multiple times. I spoke with Verizon and they could see the ONT and G3100. They remotely rebooted the G3100 and ONT, then renewed the router lease multiple times. The G3100 refuses to stay connected to the ONT for more than a few minutes. Verizon says it might be the COAX from the ONT to the router, but I doubt it. The COAX is no more than 20 years old and there is only one digital splitter at the beginning of the run. No splices, no damaged COAX. Any ideas?

Finally, if I can’t solve the problem, can I plug the WAN port on the G3100 into an open Ethernet port on the older ActionTec to create a second router/independent network?

Advice wanted. TIA.