Even if you own your Verizon router, I'd call them and explain the issue. They might offer a replacement, since some have reported firmware messing up their routers. Also, did you try a factory reset on it? There is a small, recessed reset button on the back of the router -- I think you have to hold it for 15 seconds and then release for it to reboot (it's been a while). If it is properly reset, the password and Wi-Fi credentials will change back to what is printed on label, and you can then change them back to your own choices.
Adding a new router / Mesh system
If that doesn't fix things or you want to use a different Wi-Fi access point, you can leave the Gateway in place, just turn off the Wi-Fi, and then add a new wireless access point plugged into any place you have Ethernet (either the port on the Gateway or any of the Actiontecs). The only downside is that the red Actiontecs are only capable of about 250Mbps over MOCA (since they are 1.1 devices) -- that's fine for my house, but some may want/need faster speeds.
I have a similar set up to you -- Verizon Gateway as the main router, plus 4 additional routers in bridge mode (1 more Gateway and 3 red Actiontecs). What I found was that all of the routers configured as wireless extenders can make more problems than they solve --> basically too much wifi isn't a good thing either due to overloaded channels. So if I were you, I'd consider buying a Wi-Fi mesh system and turn off all of the Wi-Fi on all of the Verizon devices, as a mesh system will actively steer devices from one access point to the other.
If you retain the Gateway (fixed or replced) -- tune your Wi-Fi -- my faux mesh system
If you want to retain the Actiontec routers for Wi-Fi (in addition to MoCA), you'll want to figure out which should be broadcasting (and at what power and on what channel) and which should only be MoCA bridges. You may only need two access points at all in your house. For example, I live in a 3 story house and use only two Gateways for Wifi (the 3 Actiontecs are MoCA bridges only) -- total footage on each floor is identical and the total is around 5,000 sq-ft.
- The main router is in the basement, right side of the house, 2.4Ghz power is 100% on channel 3, 5Ghz power is 40% on channel 132 (power levels are buried in some of the advanced wireless settings pages). Self Organizing Networking is turned on, so both bands have the same APN.
- The second Gateway is on main level, towards the left side of the house, 2.4Ghz power is 100% on channel 8, and the 5Ghz power is 100% on channel 157.
With self-organizing network band steering, you may only need the Gateway --> one APN and the router prioritizes 5Ghz and only connects devices at 2.4Ghz if the 5Ghz signal is weak. My house is a little too big for the one router, so by turning the 5Ghz power down in the basement to 40%, the devices that are connected to that router will switch over to the main router when they are in the upper level of the house. I also selected less crowded channels (all of my neighbors are on 1, 6 and 11 -- so 3 and 8 have only a little overlap to them). This is what mesh networks do, but they actively steer devices from one access point to the other, whereas this is a more passive approach. I have to leave the basement 2.4 Ghz on 100% as that provides the guest network (and our 3 teens have many guests over, pre-COVID), and I didn't bother tuning the 2.4Ghz power settings on the main level since only a few devices use it and most of those don't move around (e.g., Ring doorbell).
