This is almost assuredly the device instance vs data instance problem that Maretron have more-or-less ignored for years. I’m going to guess that both of the BMVs have the same device instance. You might be able to get things to work better by changing one of them to a different instance number.
I have a lot of Ruuvi sensors as well, and I can see those on my NMEA 2000 network, but I believe I am using Signal K to put those on the network. I’d have to go back and look since I have quite a few things on my network 