Thank you for your help!
So to do this in Modo, you need to delete the UVs entirely, recreate them (Atlas projection) and then unwrap [in Modo] the result.
I’m sure there are many reasons to make RC a bit more finicky on how it takes OBJ imports, but from my perspective, I really wish it just let me load the OBJ file as it did before the update. Maybe just throw up a warning rather than preventing me from loading the model at all.
Here’s why: I’m working in Valve’s Destinations, so I’m popping a scene out, working on it in Modo, throwing it back in RC to unwrap and re-texture and see how well my reconstructions is doing as a spot check. I seem to be getting the UV error every time I add a new element to the scene, and now I have an extra hours worth of letting Modo rebuild and unwrap UVs every time I want to see how my changes to the scene took. Unless I find out some button I should be pressing, it’ll add a lot of extra work to my workflow to get to a final product. I’d much rather do the UV remapping at the end of the project rather than with each iteration!
Thanks again for this information - wouldn’t have figured it out this quick without your feedback.