My guess is you have one SSID for both bands. I have the same thing and I just connect all my wifi devices to the single SSID - 2.4 and 5.0.
change the name of your 2.4ghz band seperate then of 5Ghz
for example is use
BiFrost for the 2.4Ghz devices and
BiFrost5G for 5Ghz..
That way you wont have to rely on band steering, and devices you connect to BiFrost5G. will only be connected at 5ghz and visa versa