Comment 2 for bug 1843793

If we can find something in wpa's log (however one gets them) and an upstream fix for that, that would be great. If you can, I suggest you try to git bisect the upstream repository from 2.6 to 2.9 and see what commit breaks it.

Please note that custom kernels are not supported, and we can't be sure it's a kernel or a wpa issue, so we'll probably have to wait for official rpi4 support if we can't figure out the cause and fix this way.