It is unknown why/how this can happen, but there are some files out there that have e.g. Objects flagged as embedded data... See e.g. the `(Anim) Hero p23 for 2.blend` file from our cloud gallery (https://cloud.blender.org/p/gallery/5b642e25bf419c1042056fc6). Not much to be done, but add another checking pass at the end of readfile process to fix these.