@PS1018 I'm running into a similar issue. I have the triband setup with smart connect and out of nowhere two days ago my 2.4ghz and smart home network disappeared. I've tried turning smart connect on to reconnect devices, didn't work. Restarted the router, unplugged it, restored it to factory settings and nothing will connect to the 2.4ghz band. I have an open support ticket, but I'm not sure what is going on as I didn't change any settings, it just occured on a random Sunday where all 2.4ghz only devices went dark. At a loss as I've tried so many different settings. Open to any ideas on here. 

  @Toomuchjohnson 
Hey, mine hasn't done this since around the time I last posted here. Before, it was almost daily. 

I believe for my situation, changing the SSID's of each of the bands to their own name SEEMS TO HAVE fixed the issue (before I had them all as AbrahamLinksys)

I'll post some screenshots of my settings below, and hopefully it'll help you solve the issue. I am not able to determine what change for sure fixed the issue.

Wireless -> Wireless settings:


(transmit power high, channel width 20/40/80/160/320 MHz)

Wireless settings -> additional settings:

  @PS1018 Thanks for the suggestion. I hadn't tried that yet. Unfortunetly, I did it now, and still no dice. The TP app shows a connect to 2.4ghz button, and it fails everytime. I can't see it when its not hidden on any device, and I hide it and tried to manually enter and that didn't work either. After all of the extensive testing I've done I can almost say with full confidence that 2.4ghz and 6Ghz have a hardware failure. It didn't make sense at first, but after days of trial and error, multiple reboots and even using a 10 year old router that's built into the moden from an ISP that worked, it's dissapointing the TP unit didn't last more than a year. I do stress it with a lot of devices, but still, I got it for that reason. Appericate the tip again, I'll circle back with support and if it ends up somehow being software, I'll update on here.