I've been testing Pix4D for photogrammetry. I've successfully brought models built with it, including textures, into Sketchfab. E.g. this one:
However I've got one that loads fine in Meshlab, but is being mis-interpreted in sketchfab, so the bits of the texture are all muddled up:
What should I check? Both are 16K textures (for better or worse - I gather that sketchfab may work better with smaller textures, but I think that's about performance rather than correctness).