https://forum.netgate.com/topic/58423/intermittently-losing-net-access/9

Its a long lived sometimes mentioned FreeBSD error that seems to occure from time to time depending on hardware.
Disabling MSI is mentioned in possibly solving the problem (hw.msk.msi_disable loader tunable).
I assume you would stick „hw.msk.msi_disable” in a config file to try it.
(That is literally just google talking as I have never actually seen this myself)

A little edit here.  Might also want to try increase size of mbuf.

And take a look here at a post by stephenw10 much earlier:
http://forum.pfsense.org/index.php/topic,57238.0.html

„The new drivers didn’t help in the Watchguard box with that same NIC.
Instead try disabling MSI for that interface. Put:
Code:

hw.msk.msi_disable=1

In the file: /boot/loader.conf.local
You will probably have to create that file.”

I think doing both the MBUF increase and disabling watchdog in MSI will fix your issue.
Perhaps someone here will have actually had some experience with this.

so in    /boot/loader.conf.local    I would but both:
kern.ipc.nmbcluster=131072
hw.msk.msi_disable=1

Just get to two possible issues out of the way.