iPhone 17 can't connect to 5Ghz wifi after iOS 27 upgrade

I'm noticing this issue with my iPhone 15 Pro Max on iOS 27.0.1. Started when I noticed I was only connecting to 5Ghz on some Unifi APs in my house and when I was in another area only serviced by 1 AP on a 5Ghz only SSID I couldn't see the SSID and my phone was switching to cellular.

I did some testing with Unifi 5Ghz radios on 80 Mhz channel width and stepped through different settings and channels. I found that I could only connect or even see the 5Ghz only SSID on channels 149 to 161. Anything lower than 149, even outside of DFS channels eg non-DFS 36-48, the SSID was invisible to my iPhone. My phone couldn't see the SSID on any of the DFS channels either.

I replicated this on GL.iNet device as well. My phone would only connect or even see the SSID if the 5Ghz 80Mhz channels were 149, 153, 157 or 161.

Dropping to 5Ghz 40Mhz channel width made no difference. No other settings made a difference to visibility or connectivity other than changing the 5Ghz channels to ones in the range 149-161.

To add to troubleshooting I'd tried, network reset on my iPhone 15 Pro Max. Device full restart. No difference in my original problem area.

Something is definitely messed up with WiFi 5Ghz for some devices on iOS 27. Going to see if I can get some other devices to test different 5Ghz channels with.

the iPhone 12 and 13 do not have the new N1 network chip that was introduced with the iPhone 17, so they may not have the same issues. I have also now seen those with iPhone 18's (with the same N1 chip) complaining of wifi connectivity problems. I installed the router and there is no MAC filtering, access control rules/restrictions, etc. Since everything works fine with iOS 26 using the same phone and router with the same network configuration, but fails with iOS 27, I suspect that there may be some compatibility issues with some older wifi 5 devices and phones with the newer N1 chip. It may be specific hardware combinations that fail, so reports may be sporadic.

Quote: Same issue here on my daughter's iPhone14.

Hmmm, that rules out the N1 chip being the problem. I'm sure both of you have thought of this, but is there a router firmware update available?

As Lobsterghost1 posted, report it to Apple using the link he provided.

Try testing elsewhere; testing with something not running DD-WRT.

Some previous reports of DD-WRT, iPhone, and troubles with 5 GHz:

https://forum.dd-wrt.com/phpBB2/viewtopic.php?t=338359

https://www.reddit.com/r/DDWRT/comments/uhvgcr/i_cant_connect_to_5ghz_band_on_most_my_devices/

Same issue here on my daughters iPhone14. Was perfectly fine connecting to my 5ghz networks before the update to ios27, now it either doesn't even see the networks, or disconnects after a few minutes. Got 30 odd other devices that have continued to function as before so I know its not my network, which is a full unifi stack. Other iPads connect fine too.

Still the same on 27.0.1

I think you did a LOT of troubleshooting. I'm on iOS 27 and not having any issue connecting to the 5gHz on my Linksys Mesh Network.

I'd recommend providing feedback to Apple so they are aware you are having an issue and you can do that here --> Feedback - iPhone - Apple

This appears to be a device-specific issue because my iPhone 12 Pro and iPhone 13 Pro are able to connect to both the 2.4 GHz and 5 GHz Wi-Fi networks without any problems.

I would recommend contacting the agency or technician who installed the router and asking them to review the router's configuration. Specifically, they should check whether any MAC address filtering, access control rules, device restrictions, or security policies have been enabled for certain SSIDs. It is possible that your iPhone's MAC address is being blocked or restricted from accessing the 5 GHz network.

Since your iPhone is unable to connect to the 5 GHz SSID while other devices connect successfully, the issue is more likely related to the router's configuration rather than the Wi-Fi service itself. The installer should also verify the router's wireless settings, channel configuration, band steering settings, and any device-specific restrictions that may be preventing your iPhone from joining the 5 GHz network.

Wi-Fi 6 or Wi-Fi 7? (Bugs in MLO implementations whether AP or client wouldn’t surprise.)

GSYoung wrote:

... after upgrading to iOS 27?

Not every issue an individual encounters on their device can be attributed to an iOS update. If the update itself were the root cause, then every device running that same version of iOS would exhibit the identical problem. In such a scenario, the forums would be flooded with countless posts reporting the same malfunction, creating an unmistakable wave of complaints that no one could possibly overlook. The absence of such widespread reports strongly indicates that the issue is not systemic, but rather specific to the device in question.