It’s an asynchronous function, so the upload will continue even if your connection is slow or gets interrupted. The UI will stall, but the process will continue in the background, that’s why it felt like it worked immediately when you tried again.
The image upload was already completed and the duplicate detection function just had to pick the image name (its hash) to generate the embed link.
Thank you, AOU. I presumed that to be how it works as the re-upload had completed immediately without any delay. I figured the initial stuck upload overlay not completing the uplaod was on my side due to my slow net and old browsers and such, but this post sounded similar to what I encountered and thought it might be more than just my local issue.
However, I re-read the other comments on the post just now and I realize that I had misread the reported issue previously. I believe the reported issue is that the actual upload button was not appearing for him on the upload overlay after selecting a local image, not that the upload overlay was stuck uploading the image as I had encountered.
I'm glad what I encountered still continues to be only a local issue for me due to slow, unreliable internet and not an instance of a bug.
(post is archived)