The times that I’ve seen this happen is when a manufacturer releases new revisions to their hardware and support hasn’t been added to Linux yet.
Looking at the latest and greatest kernel at Making sure you're not a bot! , the product ID 1790 still isn’t listed.
I looked back to old Linux versions to see if they ever did a wildcard probe on product IDs that might have made 1790 work. I don’t see it though.
Could it have been that you tested with a different USB-to-Ethernet adapter back when it worked? Maybe it was a 1780 back then.
The fix might be pretty simple. What I’d do is copy paste the lines for the 1780 in the link above in the kernel source and make an entry for the 1790. That will at least get your adapter enumerating with the ASIX driver. Hopefully the new part is backwards compatible with the 1780 and will “just” work. If that’s the case, then create a patch and include that in your Nerves system. You could also contribute it back upstream to the Linux kernel if you wanted.
