I am having the same problem more often than not. Sometimes an upload takes a lot of time while in Queue status, and sometimes it gets timed out, and fails for various reasons such as Server not responding, Invalid CSRF token, etc. It's very annoying.

@Cparle OK. Thank you.

@Cparle I could not test it on Beta, because I didn't have an account on it. Even though I just created an account on Beta, I still could not use the UploadWizard, as there are additional requirements that must be met to become an autoconfirmed user. Thank you!

So, here are the steps to reproduce the bug. 1) Upload an image 2) Give it a file name/title "somename1.jpg" 3) Publish the page 4) Click on "Upload more files" 5) Upload a different image 6) Give it (accidentally) the same file name/title "somename1.jpg" 7) Publish the page. Due to the bug, the second image overwrites the first image on the first published page. The second page is never published.

I've just performed a test with entering an existing category this time. That part is actually not significant, so it does not matter whether or not a category exists. Here's the resulting page: https://commons.wikimedia.org/wiki/File:Wikimedia_Upload-Wizard-Bug-Test_2017-11-07_(3).jpg