@HondaTom
Thanks for your reaction.
It seems like some of your actions 'triggered' the 'Optimize your network' flow, what could result in the change of the SSID.
Question: Was your modem already configured to 2 seperate SSID's and was it already working for a while?
Or did you first tried to change to seperate the SSID's like you mentioned , and then did the reboot?
Advanced Settings/Wireless/Wireless signal/Smart Wifi/Disable Channel Optimization
I did this and rebooted, after which the name of the 2.4 Ghz network was reverted to that of the 5 Ghz network, so the problem persisted.
If you only did a reboot, it could be a bug and this should not happen.
If you first changed the SmartWifi settings and then did the reboot, i think you missed something in that process.
I see your network is seperated now. This should not happen again if you reboot your modem for the next time.
p.s.: I still think your devices should also work fine with the same SSID, but maybe with a (better) workaround. I can't advice you because we don't know the details why you want to seperate your SSID exactly.