Platform & hardware limitations
Channel bandwidth not supported
This is a huge limitation, but the Windows 10 UWP apps currently can not detect this because the API's (Application programming Interface) are not present. Hopefully Microsoft will add these soon... my app is already ready for this ;) .
Link-Speed not supported
This depends heavily on your hardware, basically the Wi-Fi adapter driver which sometimes report the actual throughput (what is necessary for the Link-Speed to work). I got this info from a Microsoft developer who contacted me about this.
On the phone side it seems the Lumia x30/x35 line supports it but the x20/x25 does not. As far as I know, the new Lumia 950/950 XL does not support it (I don't have this phone but I've got feedback from users).
On the desktop side, I honestly have no idea.
My app has nothing to do with this, so there is nothing I can do to fix it... this is hardware related!
Detection of unsupported bands of a Wi-Fi adapter
It currently is impossible to detect whether a Wi-Fi adapter is capable of a certain band so I could prevent the user of switching to it. For example if your adapter is not capable of 5 GHz (and there are many out there which are not), then I would have preferred to not give the user the choice to switch to it because it will not find any networks anyway.