Colonizable Valyria Revised needs an update?

A possible reason for this...
Perhaps the Dev has fixed it now, idk, but I had the same issue a few years back with the 2.1 non-MB version.

I noticed the CTD happened whenever a navy tried to move through the Lower Rhoyne river tiles - anywhere from 1-3 months after startup. To fix this I had to edit the major_rivers in default.map file.

I can't remember now exactly what I did (sorry) but I would recommend you open the definitions.csv file in the map folder.
Then search this file for the tile numbers listed in the major_rivers section of default.map file, specifically with regard to both Upper & Lower Rhone lines.

I think I removed or #hashed out one or two of the erroneous tile numbers in the major_rivers section.
I can't really remember but I think one of them was actually one of the newly added westeros provinces added in the latest main mod update at the time.

I hope this helps, I can't check myself to verify rn

EDIT: Best way to check if it's the same issue for you is to start a game as one of the volantene counties along the rhoyne and immediately raise ships, move them along the river to see if it a CTD happens.