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