@jra11500 

Hey

In short answer, this is not an unexpected behaviour and unlikely to be changed by any firmware update.   

You can have as many SSIDs as you wish, IOT, Guest, HOME etc.. but ultimately they are all coming from the same radio (the actual chipset inside), therefore if you disable the 2.4ghz on one SSID it actually disables the radio and affects ALL the SSIDs.

The only way round this would be to have a dedicated radio chipset for each SSID, while vendors do have devices with mutiple radios, they come at a price premium and generally are not at home grade users due to the high costs involved.   From experience multi radio APs are easily over £1000 for anything semi decent

IMHO.. this is unlikely to ever be implemented at home grade hardware, other vendors are the same from experience.

  @Philbert 

Thanks for your quick response. Understanding that one chipset handles multiple SSIDs, I believe the answer here is not to actually disable the radio but rather to prevent (not hide) the SSID from being transmitted, effectively "disabling" the network. The chipset could still transmit other SSIDs keeping the radio enabled.and any other networks would then remain active.

  @Philbert 

I forgot to add that the chipset could disable the radio once the last "enabled" SSID is disabled. As long as there is at least one SSID active, the radio would remain on. That shouldn't be too hard to implement.

  @jra11500 

Hey again

While that does make sense, its sadly not how this works in practice     At a very high level..

The radio literally just takes a command and chucks it over the two frequencies.  Think about a radio as really just a conversion device for electrical to airwaves, literally it duplicates the command it gets to both frequencies.

So the chipset is asked to create SSID1, it does so twice on the 2 frequencies it knows, namely 2.4 and 5ghz.  It wont differentiate between the two frequencies at all.  One in Two out..

To get seperate commands for each frequency, we would need 2x radios, one dedicated for 2.4ghz, other for 5ghz.    This used to be common place but now is not so as it has a few downfalls (also costs more).  

The main issue is band steering and roaming.   If you have two physically separate radios, you are authenticated to radio A on 2.4ghz, and you need to move to radio B on 5ghz, for these two radios to talk and handle the handover it needs a controller in the middle.   Without some control module, A will just kick you off.. client then disconnects and then re-connects to B (or possibly A again).  

A single radio, as you are authenticated to that one radio and its aware of both frequencies.. no disconnect and no controller required.  Cleaner, quicker and cheaper

End result is that the SSID isnt done at the radio level, therefore to have different settings for 5ghz vs 2.4 would require a second chipset.  The chipset doesnt make any decisions, its just chucks out wireless signal.  The only thing it knows is BOTH ON, ONE OFF or BOTH OFF.. its that basic really.  

Sorry that is VERY laymens terms, its a very strange and difficult thing to explain

  @Philbert 

This is getting to be very interesting. On my end, I admit that I don't fully understand how the chipset functions in the router. For example, does the chipset itself actually contain the radio or does it control an external radio chip?  Same thing goes for commands... Does the chipset receive its commands from a memory (such as an eeprom) or are the commands embedded in the same chipset?  With many years of experience in software and hardware (I'm now retired), what I imagine is that the chipset receives its commands from an external memory and responds accordingly. The software should be able to control the radio, when it is on and what it transmits. There should not be any problem in controlling the number of SSIDs, after all it is done on a time sharing basis. Each band should be separately controlled and I see no problem with that either. Bottom line... The solution is in the software (firmware) and the hardware will respond accordingly.