THE MYSTERY DEEPENS!
so, after going back to my OSX machine, all kinds of stuff didnt work anymore. i wasnt getting midi data from almost anything, my midi monitor app showed nothing coming in from the motus... I was stumped for a couple days. but then i remembered something i saw offhand in Clockworks OS9 that had me thinking...
so i opened up the two side by side, OS9 and OSX versions... and they're different!!
the OSX version has absolutely no provision for setting up routing to and from the second computer. it appears that by default, almost nothing is being routed to the second computer. In Clockworks OS9, I went in and manually drew out all the device connections (as shown in red in the third picture) for both to and from devices.
This fully solved the problem, finally. both OSX and OS9 machines attached to either end of the MOTU network are now working 100% without issue. the only head-scratcher remaining is how *some* devices had existing routing from the second mac port, but not all of them. i didnt do that myself, at least, not intentionally.
it seems pretty wild that MOTU would have completely removed the ability to edit routing to/from the second computer. and its not a matter of it not seeing it, if you look in below the transport bar it shows the firmware for both units, the second one being noted by "NET" in front.