iCloud has trouble authenticating when using my XD6 router

[JCRoswell]

A few months ago I bought the ASUS ZenWiFi XD6 (AX5400) system, and it works great except I have an issue with the iCloud service. iCloud constantly gives me the error "An error occurred during authentication." This only happens on my home network. It happens for both my desktop (Win10) and my laptop (Win11). It does not happen to my laptop at work, or to either computer if I use my phone's hotspot. So, it appears there is something in my router setup that is causing this issue.

Any ideas of where to look or what could be causing this?

Things I've tried:

• Turning off the router's firewall
• Turning off AiProtection

Any direction would be appreciated.

John