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.