Hi,
I have seen such reports in the past, but settings depend on Router Model
I personally own pair of ASUS RT-AX92U Routers and use
ASUS Smart connect that allow same WiFi SSID name so it does not matter if you are connected on 2.4ghz or 5ghz WLAN.
I suspect that it is settings issue and possibly that you have AP Isolation enabled (Some routers have that enabled by default).