Hm, in that post they say all of the 2.4ghz devices had the problem, while in my case it was just the iPad, and it was broken on both bands. But maybe it still was this (or a similar) issue. I only have access to one of the two APs right now, and there is pretty much nothing configurable regarding WiFi security apart from selecting from WPA1+2, WPA2 only, WPA2+3.