Hanging upload

I tried to upload an image, and got an screen saying "This upload is being processed. Please wait a few seconds." After this, the tab kept refreshing every few seconds without any changes, seemingly indefinitely.
Later, I uploaded that image again, this time without problems. Now I don't know what I should do with the first upload.
Here's a link to the upload: https://danbooru.donmai.us/uploads/1010366

This has happened to me before. Since you were able to upload it without problems later, then the first attempt will give a "MD5 taken / this image has already been uploaded" error once it finally finishes processing.

Happened to me a bunch of times. I just try again and that usually works.

Yeah, if either of the two situations happens, the problem usually resolves itself. In the event that an upload gets corrupted, flag the broken upload for deletion and/or hit up a Janitor or Mod and they can delete it for you.