Site-to-Site IPSEC suddenly stopped passing traffic

Question

I have had a Site to Site IPSEC connection established for years and all of the sudden it has stopped passing traffic... 
 Both systems UTM 9.509-3 
 Here is a tcpdump of the source (Respond only GW) UTM ipsec connection: 
 
 here is a tcpdump of the destination (Initiate Connection GW) UTM ipsec connection 
 
 You can see the traffic go out, hits the destination, and when the destination replies, you do not see the reply back on the source... I am using auto firewall rules and nothing has changed on either config short of just patching the UTMs. The connection is showing Green in Site-to-Site. I am at a loss for what could have suddenly started to cause this issue... 
 Any thoughts...?

BrianGleason · Accepted Answer

Weirdest %$@# ever... I reset the router, there is actually an edge router that sits between the destination edge and the internal sophos device, and even though the IPSEC connection was getting established through that device, it was not passing the traffic back. After reseting that edge device, all was right with the world... Messed up, but I guess ok...