Never get "wifi authentication" prompt from Aus routers, using GT-AX6000 + RT-AX86U, both running Merlin firmware with adguard. Mate20X is my secondary phone, using everyday, tested with Zero1, ZYM and MY's Hotlink. No problem whatsoever, still fast enough for everyday app, frquently downloading/streaming 2 security videos simultaneously.
Try manually setting IP for each device thru router DHCP server.
Just me, the OLED color is getting overly saturated with max brightness--but that's me being critic about color accuracy. Also keep getting selection draw instead of press, had to disable the very useful double knuck screen capture.