Ethernet connection to Mesa 7i76e disconnecting on its own after one minute

So does that mean you are in business and have a PC for spare parts? Hope so!
If not, I might be able to work in another site visit but it would cost you some footage for a YouTube video... 
There is an email that gets me on my @MrRodW YouTube channel

I should note that I have a HP EliteDesk 800 G1 that could never run Ethernet cards reliably
 for more than an hour or so UNTIL I upgraded the kernel to 7.x

It also requires:

disabling irq coalescing
isolcpus=3
and pinning the Ethernet IRQ to CPU 3

With these changes, I never get dropped packets even after months of uptime
with a PC used for compiling, youtube etc etc