Intel has had a somewhat awkward relationship with FreeBSD forever. While they are forced to support it (for $reasons) they never have properly covered it.

I would say as of FreeBSD 12-13 most major issues are addressed from 1gig up to current 100g. There is an odd bug in 2.5g igc where some users have interface stalls whilst others like Netgate are shipping large numbers without issue, waiting to hear if this is firmware or not.

Source: I maintain several of the Intel drivers on a volunteer basis and used to send several Tbit/s to the Internet over them professionally.