I'll see if I can borrow a switch somewhere, but nobody I know offhand has one, and I'm trying, as much as everyone else is, to limit who we interact with. I'll have access to a new, unopened AX88U tomorrow, and I've been reading that I likely want one with the 1.1 version (if that's not right let me know), I don't recall what the build number is on the one that I have at home, and hopefully I'll get a chance to take a look tonight -- and since I stayed up last night determined to get it working and didn't I'm dead tired, LOL.If you have another router or can borrow a switch, I'd put the switch between your PC and router LAN port. Or between your modem and router WAN port. Disable DHCP on the router that you are using as switch first.
I've seen some routers just not get along with some Ethernet devices that work just fine with other routers. Something in the way auto-negotiation works. Even forcing the speed/mode of the device port didn't help.
Worst case I'll report back once I get the new (mine was new too) AX88U tomorrow and maybe by some stroke of luck it'll work.