I've got the same problem as the image linked in that post shows.
"The mesh <mesh name> uses ' ' as a material, but no m3 material of that name exists!"
After each attempt, it also 'clones' the mesh of my model, and i can't remove it without removing the entire model.
I've tried everything and anything i could think of on my end of things, but it still won't export.
Did anyone actually have this problem and actually solve it?