This is not a regular problem and I don’t think IPFire is the reason for it because I use the same chips (not only once) and don’t have the problem.
Also you should check the firmware of your X550 for updates: Non-Volatile Memory (NVM) Update Utility for Intel® Ethernet Network Adapter X550 Series
There have been problems with buffer overflow.
Also your green network is working with 10G, because the output shows “Speed: 10000Mb/s”. Your red network probably doesn’t work with 2,5G because your transceiver does only work with 1/10G. Only newer transceivers work with 2,5/5G as well.
Edit: 2,5/5G is not listed for Advertised link modes that are used for Auto-negotiation. That may be also a reason why your red network is limited to 1G.
Is this an T2 or AT2 card?