One of our customers recently updated firmware on their NSA2400 and the wan connection began to die as well as the actual firewall appliance becoming unresponsive.
So i thought the unit was faulty as I put a TZ210 in it's place with same config and there were no problems.
I couldnt troubleshoot this during working hours as the customer had a lot of vpns etc. that needed to be up to run their business.So I came in on Saturday and myself and the customer turned off auto negotiate on the wan port and set it to 100Mbps full duplex.
Problem solved!! It was connecting to a Cisco router and that was causing all the fuss. A really simple fix but one that could drive you crazy!