I recently changed the stock firmware on a TP-Link Archer C20 (Router and Wireless AP) to OpenWrt 22.03 and configured it as a "Dumb AP" on my home LAN, as per the instructions on the OpenWrt website.
All my devices seem happy to access the LAN via 2.4GHz radio or 5GHz radio except my Apple iPhone 7. I have plenty of other Apple devices that can connect and see the LAN on 5GHz, although it might be worth noting that they are all older than the iPhone 7.
The first sign that there was a problem was when I moved into the room where the OpenWrt router is located and my phone lost internet connection, although it was still connected to the AP. At this stage, I had configured the 2.4GHz and 5GHz radios with the same SSID, so the iPhone would automatically switch to the 5GHz radio with the same SSID when I entered the room and switch to 2.4GHz when I left and moved away from the AP.
When on 5GHz, my iPhone would be unable to access the LAN, and therefore was unable to get an IP via DHCP. After a long attempt, it would give up and assign itself a 169.254 address. Even if I manually assigned an IP on the iPhone (disabling DHCP client on the iPhone), I was still unable to access any machines on the LAN from the iPhone. Note that the AP is not running a DHCP server, as described in the "Dumb AP" setup instructions from OpenWrt. My gateway (Ubiquiti EdgeRouter) is running the DHCP server.
On the AP's Luci UI, I can see the iPhone connecting on the Network->Wireless "Associated Stations" list, but it cycles between appearing and disappearing on that list (on wlan1, the 5GHz radio).
No other devices have a problem connecting to the 5GHz radio, seeing the LAN and getting an IP from the gateway via DHCP.
I have since assigned a separate SSID to the 5GHz radio, which confirms the the problem in only when connecting on 5GHz, and only with the iPhone 7.
The OpenWrt AP is replacing a dual-band ASUS AP, which the iPhone had no trouble using on 5GHz.
I would appreciate help and ideas to solve this problem. I am stumped.