Thank you for all the responses, so I have tried to get more information in this issue:
So far core 172 is working great, even considering the issues when I downgraded.
I wanted to get to the core of the issue why did it fail with core175:
I have a few of these Realtek cards, they are identical just few months old. I used them briefly with PFsense/FreeBSD and debian.
Again these show up in IPFIRE as “Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15)”
So I got another old desktop and put a 3rd Realtek NIC (never used with IPFIRE before. )
I tried to recreate my issues:
- I installed core 172 and assigned
RED: Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 15)
GREEN: built in Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 0)
The desktop had a very similar NIC built in - the only difference seems to be (rev0)
and the GREEN NIC worked great. this is the built in Rev0
the RED NIC got assigned without issues but it couldn’t get and IP again. this is the Rev15 , that I just installed and it works fine with Debian, PFsense.
so this can’t be caused by a hardware issue, or damage, just something with this particular (Rev15) is not working properly, I looked for system logs for RED and it wouldn’t show anything unusual.
I tried to reboot, without success and I tried 2 more reboots and after 3rd reboot RED interface finally got an IP assigned. 
Just like that, started to work properly.
Then I upgraded to core 175, this time I had zero issues, and both NIC’s are responsive. all works great.
So if you want to save yourself headaches, avoid this particular Realtek Rev15.