Try with just WPA2. see this if > 1 SSID on a radio.
Avoid DFS channels, at least for testing. Using DFS channels implies at least 60s wait time before the channel may go up - and mwlwifi has never been good dealing with DFS to begin with (meaning it may fail if a radar is detected).
it's been a day and there isn't any radar on this frequency around here (plus the AP is in the basement)
FYI, I tried with openwrt-22.03.0-rc6-mvebu-cortexa9-linksys_wrt1200ac-squashfs-sysupgrade and also had issues with 5 GHz using WPA2-PSK/WPA3-SAE Mixed on WRT1200AC v2. I rolled back to openwrt-21.02.3-mvebu-cortexa9-linksys_wrt1200ac-squashfs-sysupgrade and everything seems ok now on the 5 GHz.