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You need to triangulate all the faces. You will notice after that error that bitcpy's script selects/highlights the n-gons that need to be triangulated.
In edit mode with those faces selected (or all faces), do Mesh -> Faces -> Triangulate Faces.
Model/animation import seems to not quite be accurate for many or most skinned animations. For example, lindworm_fly_maneuver_1.animation fails to move some vertices:
Of course this isn't a big deal since animation export doesn't support bone animations yet anyway.
Hmm, you're right, I just tried importing and immediately exporting an animation and it worked fine. I could swear I tried that before and it didn't work (only used the first keyframe and then didn't move the model for the remainder of the animation). Guess I need to figure out what's wrong with my own animation. Never mind.