I have a flat class C home network. My network consisted of an Asus router and four TP-Link range extenders: Three were RE605X's and one was an RE700X. For the past six months I've had "gremlins" on my home network that I couldn't track down. I even replaced my router, thinking it was the issue. Eventually I discovered via traceroutes that when my network issues surfaced, the affected machines would have two hops to the router. The first hop was a TP-Link extender, the second was the actual router. The first hops would alternate between my three RE605X's. Investigating further I found in my ARP tables that the extenders were spoofing the MAC address of my router, causing the router to hit them first. This happened to my wired and wireless devices. I removed the RE605X's and kept the RE700X and the problem went away for a while so I figured that one of them had old or bad firmware. Unfortunately I lost the password to the one that I thought was the problem and I can't log in without factory resetting it, which means I'll never see if the issue was a configuration setting or what.

Anyways, the problem has resurfaced with only my RE700X in service. One of my PCs was having intermittent connectivity and a route print showed that it was hitting the RE700X before hitting the router. This PC is wired, Windows Server 2019.  Why does this keep happening and how do I fix it?

Below is what it looks like when the problem occurs: