Cisco Wireless :: 2504 WLC / Flexconnect APs Stopped Joining?

A customer of mine has a centralized 2504 WLC with 7.2 code running.  They have 1142N APs deployed locally as well as in remote sites (3) in FlexConnect mode.  For no apparent reason last Thursday all the remote APs disassociated with the controller and could not rejoin.  All the local APs remained up and unaffected.No changes to the WLAN, LAN, Firewall or MPLS WAN occured to cause this.The customer opened a TAC case and their determination was that ports 5246-5247 were not getting thru.  When the customer engaged me this morning I had him run a packet capture on the Sonicwall firewall to prove out if the CAPWAP signals were leaving and returning across the WAN.  Sure enough we can see this bi-directional traffic (pic attached).  Also, I had the MPLS provider run a trace at the far end and they see the same traffic leave the remote site.  And then an odd thing happened; one of the APs at one of the remote sites all of a sudden Joined the controller.  So I tried rebooting the AP that is located in the same office, and it fails to Join.  When I look on the controller under AP Join statistics, the last activity shows the controller receiving a Discovery Request and response is sent, but no further Config Request and response or Join Request and response.