The find_best_vertex_split function iterates over all vertices:

However, immediately after the loop, there is an assertion that best_split_index may not be the last vertex:

While testing file sizes of different formats, I've encountered a model that apparently meets this edge case, resulting in an assertion error.

This is the mesh I am trying to export. It's the dragon sample model from the official glTF samples with computed tangents, run through meshopt: dragon.zip