Hello, I have a similar problem, one of the fiber interfaces on my Intel x520-da2 drops and comes back after some time, were you able to solve your problem?
I wonder if it is driver-related: as I understand it, VyOS 1.4 and 1.5 both use the in-tree Linux Kernel ixgbe driver by default, which is not the same as the ixgbe driver provided “out-of-tree” by Intel.
My experience with ixgbe and VyOS is limited to the newer X553 interface, where I encountered some link issues with the in-tree ixgbe driver, similar to what is detailed on this thread.
@samip537 there was building 1.4 images incorporating the very latest ixgbe driver from Intel, and making them available here. If you are OK with testing with one of those, that might shed some more light on the issue.
In this particular case it isnt the same which is a shame from Intel point of view and sucks.
A quicktest is to boot on latest FreeBSD and such to verify if you get the same error there or some other way use a linux dist who uses the out-of-tree driver and liveboot that just to rule things out that the error isnt hardware related or related to what sits on the other end of the cable.
The search engine over at https://vyos.dev seems to currently be broken but Im pretty sure there already exists a task to switch to the out-of-tree driver for intel NICs in VyOS.