Sometimes the composition property is missing in the metadata and then a track is not considered a composition. It’s a PITA. See here and the link to an older thread from there (as well as the further links from that link I posted there):
Sometimes the composition property is missing in the metadata and then a track is not considered a composition. It’s a PITA. See here and the link to an older thread from there (as well as the further links from that link I posted there):