I wrote a very simple script using 802.11ac with active probing enabled (no traffic, just a station trying to get associated to an AP). I see a flow of probe requests followed by probe responses, but no association request being triggered.

I added some more traces, and I noticed this return (in StaWifiMac:Receive) was hit because rates are not matching:

          for (uint32_t i = 0; i < m_phy->GetNBssMembershipSelectors (); i++)
            {
              uint32_t selector = m_phy->GetBssMembershipSelector (i);
              if (!rates.IsSupportedRate (selector))
                {
                  return;
                }
            }

This is not seen with legacy standards (a/b/g), but this only occurs for n and ac (and I guess ax as well).

I will investigate this issue.