Same problem for us, when upgrading : a lot of 2.4Ghz clients are not be able to have the IP : I saw 0.0.0.0
But when using the release Software: 10.31.08.0006 : everything is OK
10.31.X is OK
but 10.41.X are not ok (trying the three last release whit same problem)
I did some more testing again with some tunnel debug commands, they showed nothing, then I did a RealCapture on the AP and it doesn't see the client's probe requests at all.
I have not, I see "wns0021104 Corrected 2.4GHz rate selection on AP38xx for single 1x1 clients." in the release notes which is interesting, although the symptom I see is the AP can't hear the client, not the other way around. I'll see if I can find some time to give it a try tomorrow.