iabd wrote:

The modem is an Arris, model TG1672G

That is a modem router. Two routers on your network can cause headaches. For example, you can end up with local address problems. Among other things, the other router can misdirect addresses that the Netgear router usually handles, such as routerlogin.net or the usual IP address for a router, 192.168.1.1.

This explains some of the other drawbacks.

What is Double NAT? | Answer | NETGEAR Support

It could also explain what you see. And disabling the wifi on the Arris does not disable the router.

Unless you have specific reasons for using two routers – to create two separate networks for example – it is often easier to use just one router and then to set up the second router as a wifi access point. Netgear advises this, as does just about every site you will visit.

It may be possible to put the modem/router into modem only (bridge) mode and then to use the second device as the router. Sometimes it is easier to put the second router into AP mode. But that has its own drawbacks:

Disabled Features on the Router when set to AP Mode | Answer | NETGEAR Support

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