Ha ! I've met that, too. ( PP_11.3)

I got shadows etc, and managed to 'see' the mesh using several of the outline etc display options. Problem is the FBX did not designate any parts or groups as having materials / textures. And to many programs, without such, itsa ghost...

I've also seen it happen with eg an OBJ mesh that did not correctly designate parts or groups. At least an OBJ is a text-file, open to inspection / editing with Notepad or, if over ~100k, Wordpad. Latter, incidentally, will handle multi-meg OBJ files without complaint. This access is essential when trying to figure why an OBJ will not call its companion MTL file. First few lines usually show (1) exported from Blender and (2) hard-coded to eg "mtllib C:UsersSteveDocumentsSteve's 3D filesPlanet ArchipelagoAlien Gourd TreeRuntimeGeometriesPlanet ArchipelagoAlien Gourd TreeAlien Gourd tree.Mtl" instead of portable "mtllib Alien Gourd tree.Mtl" {Facepalm...}

I'm not familiar with Maya, know very little about Mixamo, but I think you may have to go back to those, 'group' parts and re-export. Watch the default I/O options...

FWIW, it is possible to do 'grouping' within Poser, but I find that tool's UI, um, quirky. YMMV. There's info in the ~1kpp Poser_11 PDF manual... Group Editor ~page 994