I received my gl-axt1800 last week and manage to set it up today for testing and review.
I notice the router can only connect to other wireless AP that use WPA/WPA2 PSK only. The axt1800 router will crash and be stuck in a loop if it configures to connect to the Access Point that uses WPA3+PSK on the 5ghz band.
This is my test setup.
wireless client → gl-act1800 (Wireless ISP) → asus ax87u (5ghz WPA3+PSK) → Internet
Same here, my for Fritz!Box 7590.
When Wifi there is set to WPA3 the Slate goes to loop. Have to push button on Slate and then switch to WPA2 on my Fritzbox to get the Slate connected.