NEW Arcadyan TMO-G4AR can't split bands

I am trying to lock my WiFi output to only the 2.4 Ghz band and turn off the 5.0 Ghz band.

I see where to select this in the App, where it gives three options: Automatic, 2.4 and 5.0.
I select 2.4, it confirms my selection, and goes offline 90 seconds and says the change was successful. But when I look at my WiFi output, it still shows it as Automatic with both bands selected. It won't shut of the 5.0 band.

Problem is, some of the devices on the far side of the house like ROKU which work on both bands will lock on to the 5.0 which barely has a signal and will ignore the stronger but slower 2.4 signal. I need to shut of the 5.0 signal completely so only the 2.4 signal will work, and this new gateway will not do that. My old Arcadyan gateway did this just fine.

I even tried creating a second WiFi network, but that did the same thing.