I have the same issue with FreeNAS 11.1-U1. I created a bug report for FreeNAS and they are looking into it, but they were a little perplexed that a newer driver for FreeBSD was available but wasn't imported into the FreeBSD repository even though Intel is supposed to have FreeBSD committers.
02) Intel(R) Ethernet Converged Network 5.05 1572 00:005 Update
Adapter X710-2 available
I am updating the firmware now to 6.01... But I am fairly certain that will not work. From what I can see in the bug tracking and googling, this has been going on for a while and either keeps coming back or never gets fixed.
From what I can see, the responsibility is on Intel to fix this for good and get the committers to imported the latest drivers in the FreeBSD head.
Intel, can we please get a permanent fix please?
Thank you for posting in Wired Communities. Can you share if the X710 is an onboard NIC or standalone network card?
Is the newer driver you mentioned refer to version 1.9.5 at https://downloadcenter.intel.com/download/25160/Ethernet-Intel-Network-Adapter-Driver-for-PCIe-40-Gigabit-Ethernet-Network-Connection-under-FreeBSD-?
What is the result of your firmware update to 6.01?
Please feel free to update me so that we can better check on this.