@ceedee 

Which mode, Range Extender or AP are you using?  Are you using OneMesh?   

Not using one mesh. using 220 as extender

i just found an updated manual that does not have the check box.  
 

Here's the issue: I have a bunch of kasa devices that must connect via 2.4. I was just going to leave the feature disabled.  Now I don't know what to select.

thanks. 

@ceedee 

How did you configure the extender?  Via WPS or Tether/Web UI?

If it was via WPS did you repeat the process so that both bands were configured?

If not then I would suggest reseting the product and reconfiguring,  I would use the Web or Tether app setup and make sure you extend both bands, this way Highspeed is not enabled.  

If that does not work and Highspeed remains enabled you can choose manual and choose the band to the router to be 5GHz this would then mean 2.4GHz can only be used for clients 

@Carl 

thanks for your input. I used webUI to configure. Both radios are enabled.  When I get a minute, I'll do a reset and start over.