Official comment
There hasn't been many upload issues occurring in the last bunch of years considering the hundreds of thousands of files that are uploaded daily.
Use the DJI Specific workflow if possible. Try using a different browser if possible. Try using a different internet connection if possible. Disable plugins. Try an incognito or private browser window to rule out issues with your browser extensions.
If all that fails but for some reason you can upload to Dropbox/Box/GoogleDrive/OneDrive you could select the images directly from there to avoid having to upload to us at all.