Also the limitation is at 2 or 3 ssids per band, one is given up by guest network, it is very possible the code works against your use case because it wants to change the interface.
Instead what you can do if you feel comfortable to do it, but requires exclusively the use of OP24 and vlans is using multi psk, then based by different password you are sent to the vlan network, currently that is what I'm using at my home, for a dumbap scenario you can use: option vlan_tagged_interface 'eth1'
You can use either the old wpa_psk_file option, or use wifi-vlan and wifi-station.
I wrote a script for this on the forum 
What doesn't work with multi psk is fast roaming, it requires a special fix/patch work and requires to compile OpenWrt yourself, WPA3/SAE requires list mac 'xxx' inside the wifi-station section and may only works on a even more recenter version of OP24 not sure if GL firmware support that yet.
For vlans I also wrote a up to date tutorial, I also like the videos of onemarcfifty.