This is a well known problem with the Intel e1000e driver since 2013.
You can easily find lots of people having this problem by searching on the internet. It is not an IPFire specific issue.
In the IPFire forum there are these posts.
https://community.ipfire.org/t/e1000e-green0-detected-hardware-unit-hang/6324
https://community.ipfire.org/t/e10001-detected-hardware-unit-hang/13414
https://community.ipfire.org/t/network-problem-with-e1000e-after-upgrade-from-core-173-to-191/13594
Several of the above posts metion the workaround which is to disable some of the offloading functions on the nics.
ethtool -K green0 gso off gro off tso off
When you reboot the nics will re-enanble those functions so you will need to add the command into the rc.local file in IPFire.
Look through the above post links and in the IPFDire documentation on rc.local