I've been trying to work out why some single band devices that can't even 'see' 5Ghz signals don't seem to like both bands having the same SSID but most are happy.
This quote seems to explain the reason quite well
It's the device you're using for setup that needs to be 2.4Ghz - the coexisting 5Ghz network doesn't actually matter. The crappy device is listening for packets broadcast on the physical layer to tell it the SSID and password, so the phone has to be on that band to send them. Which is a problem for iPhones that don't let you specify the band, so the fix is to turn off 5Ghz, not because the device cares, but to force the phone to use 2.4.
I.e, the devices are connecting in ad-hoc mode rather than via the router.
A single SSID is required for true band steering of dual band devices.
