Under heavy load internet gets killed, only a reboot can bring it back up

[Wojciech Puchar]

>
> One thing worth trying would be to disable MSI/MSI-X.  You can disable
> these by adding the following to your /boot/loader.conf :
>
> hw.pci.enable_msix="0"
> hw.pci.enable_msi="0"

what's wrong in MSI interrupts?

>> mskc0: Uncorrectable PCI Express error
>> mskc0: Uncorrectable PCI Express error
>
> Those errors at the end of your dmesg don't look good; could be the sign
> of a NIC or motherboard that's going bad, or possibly a very strange
> driver problem.

or just connectors should be cleaner or card isn't fitted well - contact 
problems.