Sounds like route tables are finding a priority match on the 1gb interface. Are you 100% sure the NAS connection is truly not an overlapping subnet with the 1gb nic?
you need to look at the routing tables on your computer. these tables store the prioritized rules for how packets leave your host machine.
it might be that something is adding rules, or, there is some overly broad rule taking priority (like a rule that says all 10.0.0.0/8 traffic go to your home router over 192.168.69.0/24, etc)
it’s also suspect that you can reach the NAS over the 1gb card. That to me means one of two things:
something is not actually using the IP you’ve configured in your fstab and is using some IP that is on the 1gb interface
you have some weird network routes configured that is leading to this issue. if 10.42.69.0/24 is accessible over the 192.168.69.0/24 network, then you might need to create a static route explicitly telling your OS to send packets out the 40gb card
ultimately, i suggest you run something like tcpdump or wireshark on your computer (ideally on the NAS too) so you can start to visualize how the packets are being addressed and transferred over your networks.
A bad route would be the first thing I’d check, too.
It sounds like u/[email protected] is already pretty familiar with the Linux command line, but just in case, you can check the routing table (on both the NAS and the client machine) with ip route (that should show the whole routing table) and get the specific route to the remote device with ip route get 10.42.69.XXX (change the XXX to make it the address of the remote system). If either side shows that the route is going over your default gateway, that’s your problem.