I've had this issue too on older devices, until I made the SSIDs different by suffixing 2ghz and 5ghz to each one. I think I've had it happen both on an older Android and older MacBook but it was a while ago, could be misremembering.
I think enough of us were running dual-band networks sharing the same SSID back in the day that doing so now cannot be the entire reason for things not working.
