@David-TP 

Hi david, thanks for reply.

Yes, I'm able stably to reproduce this issue.

Yes, I'm currently running on iOS 17.1.1.

"Deco APP>More>IOT, and set its band to 5 GHz only." on this section there is no option for me to set 5 GHz only on band option.

also been tried to set preferred Wi-Fi band on 5 GHz only, it doesnt work. Stay connected to 2.4 GHz band.

I tried to restart my deco and set it again on preferred section, and the result still the same.

But if am using the main Wi-Fi SSID, whenever i set up for 5 GHz only on preferred section on my iphone, my iphone keep rejecting it, unable to connect at all, compared to IoT Wi-Fi SSID, it still can connected but not connect to 5 GHz band, even i choose preferred band on 5 GHz only.

Another updated : 

i just noticed that on my iphone X also doesnt work properly on 5 GHz band, it keeps rejecting whenever i set it up preffered band on 5 GHz band.

on IoT Network, same result like iphone 15 PM, the iphone X still able to connect, but whenever i setup preffered band to 5 GHz band, nothing happen, stuck but connect on 2.4 GHz band even on app already preffered to 5 GHz band.

my iphone X using iOS 16.7.2

  @David-TP 

Thank you for reply David,

Yes i'm using wpa3/wpa2 on my deco X80, i also tried with wpa2 only, wpa only and wpa/wpa2 still i can't connect with 5 GHz band on my iphone X and iphone 15 PM.

If i try to connect on 2.4 GHz band, all my phone works perfectly, but when i tried to connect with preffered band on 5 GHz band, both my iphone keep rejecting to join the network.

I also tried with IoT network, still the same result, stuck on 2.4 GHz band even you try to prefer on 5 GHz band.

Hope there is an update for this very very soon!

Regards ZCX

  @David-TP 

Hi David, thanks for reply.

Usually i turn off the private address on wifi, since am using Mikrotik for bandwidth management, also tried with private address enabled and not working.

Also i already tried on Router Mode and Access Point mode with and without mikrotik, still no works on both mode to connect 5 GHz band on both phone (iphone X and 15 PM).

What i know right now, i have "M5" that broadcast only on my garage, not connected with any deco x80 or other deco, like standalone M5 without any satelitte on that network, i tried speedtest on fast and speedtest it self, i can received full speed around 300-400 Mbps on my iphone 15 PM. this M5 also connect on my mikrotik + AP mode.

best regards, zcx.