Issues with Cisco APs in local mode over MPLS ?

Hi guys,

We have a Cisco 5508 HA cluster (SSO) in our head office that provides a Corporate SSID, 802.1x certificate based authentication.

The APs at head office are registered to the WLC in local mode so the clients break out at an interface on the WLC as not at the AP - CAPWAPP tunnels and all that jazz :) no reported issues of poor performance / slow logons / network dropouts by users at head office using this SSID.

We have 2 remote offices that connect over a third party MPLS network, that also register their APs in local mode back to this WLC so the same SSID is broadcast and clients are subject to the same firewall policy based on the IP address the get etc - not reinventing the wheel, I've seen this set-up quite a few times before and it works well.

However, we are getting reports (anecdotal at the moment) of the wireless network generally being slow to log on (some clients take 20-30 mins) sometimes at these remote sites, network unavailability for short periods of time. I can't figure out what could be at play. The only thing I could potentially put my finger of was the overhead of the CAPWAPP tunnel causing fragmentation issues over the MPLS, so I dropped the MSS on the remote offices APs but we are still getting reports from users.

Any ideas on how I can troubleshoot this ? Anything obvious I'm missing ?