@Kevin_Z Thanks for that suggestion. Have done that now and it works. Much appreciated.

As an update, I believe the issue may be the router security on the 2.4/5.0ghz network. The default security is WPA3-Personal + WPA2-PSK[AES]. As an experiment, I set the 2.4/5.0ghz network to "Open"...

I just set up the Archer BE9300 as my new router to replace an Asus RT-AX86U. After setting up the wifi (2.4 and 5 ghz), I have connected all my clients (even an older ASUS RT-AC68U in Media Bridge...