That is only a warning, it is not your actual problem.
Does changing your IP period fix the problem, or only when you don't have a static address, or only when you don't have THAT static address?
Take a packet capture using the serial or SSH CLI and a firmware 2.26 or greater. Take one on the WAN and one on the LAN at the same time, we may want capture filters to protect the buffer if we have a heavy load.
pcapdump is the relevant command from the CLI, you will then have to SCP the caps off the firewall.
Take one working, and one not working.
Double points if you can get me a syslog of the time of these tests.
PM me a way to get your caps, and I will take a look at them.