I've been experiencing the same issue over the last couple of months. I've renamed the 2G SSID but I'm getting Ubuntu, Android and iOS devices all being disconnected from 5G and unable to reconnect - even though they temporarily appear in the 5G station list while they try. If I reboot or stop/start 5G they will connect fine. It can stay up for a couple of weeks, or 10 minutes before dropping connections again. 2G is fine at the same time.

From when I bought it in Feb 2023 until the last couple of months it worked perfectly, so maybe a recent firmware upgrade has caused the issue? I'm on 4.4.5.2_BT

I'm experiencing something similar but different. Posting it here to see if anyone can offer me any advice or troubleshooting tips.
Got my 2866ax a week ago. Upgraded not to 4.4.5.2_BT and set it up. Don't think I changed much from default choices. All seemed fine.
Within a couple of hours the wireless died. The only thing to fix it was a reboot.
Since then I've found this thread...so I've tried:

• Separating 2.4GHz and 5GHz
• Disabling 2.4GHz
• Disabling 5GHz

All have the same result - within a few hours everything wireless stops.
The lights on the router indicate that everything is fine.
On the client side the behaviour varies:

• No new devices can connect
• Existing devices may or may not appear to be connected (but none of them are, everything just times out - ping, http, etc.)

My concern now is whether I just have a bad box and a new one will fix it...or if I'm experiencing a firmware bug.
Any hints or tips much appreciated.

I put something similar to this reply on another post I think - but -

Do you have a Sky Q setup in the same property? - if so have a good look at how that's setup as Sky's networking leaves a lot to be desired.