Well, the problem is that in this case 2.4GHz and 5GHz bands are for the same network which is saved under the same SSID.
AFAICT you cannot directly influence that, and you'd probably need to edit wpa_supplicant.conf directly, cf.
https://unix.stackexchange.com/question ... sing-bssid@adhefe: But I don't understand the issue here, if the same router provides 2.4GHz and 5GHz bands, and one does not work, then your client should reconnect to the other one. If it doesn't then that is a limitation either for the router or in your client's firmware / wifi driver.
You'd need to post logs from a specific example where this happens, so that we could check why your client doesn't reconnect to the other band.