Sometimes it bugs out, I’m not sure why. Usually when this happens, if I close down all browsers and try again it works.
the thumbnail needs to be 512x 512 with a transparent background.
if you still have issues let me know
the issue not with the thubmail its with the glb file the thubmail already uploaded the glb file cannot upload
upload the glb first then the thumbnail. but im saying your thuimbnail isnt transparent by the one you sent earlier so it will need adjusting anyway