i think this may be the same thing as what was reported in https://forum.inaturalist.org/t/web-upload-bug-dropped-observation/76214.
if you can consistently reproduce the problem with every upload, then it may help folks to understand what’s going on better if you can capture any errors that may be getting logged in your browser’s console, as noted here: https://forum.inaturalist.org/t/web-upload-bug-dropped-observation/76214/12.