I would suggest keep checking and experimenting with the AC network, since according to this thread, it doesn’t sound like Wyze supports AX yet.
So the first 5 are connected to the AC network and working fine connected to this AC router, having been through the identical setup procedure, correct?
So maybe some obscure router setting like not enough DHCP addresses left? MAC blocking? etc?
Maybe manually flash the cam firmware to the latest version on the Wyze website to see if that helps?
If you have a phone that can hotspot and another device that can run the setup, maybe try connecting the cam to your phone’s hotspot just to narrow down the issue?