Apologies for the bad title, I can't think of a better one atm …
From [[https://commons.wikimedia.org/wiki/Commons:Upload_Wizard_feedback/Archive/2015/05#Problem_when_my_login_is_thrown_off | Upload Wizard feedback]]:
> I have experienced the following problem several times. If I am using the Upload Wizard to upload some images, Wikimedia sometimes automatically throws me off my login without telling me. If I then, without knowing that I've been thrown off, try to complete the upload, the wizard just returns an error message saying "You must be logged in to save files in the upload stash.". Yes, of course, I know that, but I WAS logged on, you just threw me off automatically without telling me. What's really annoying is that the wizard doesn't allow me to fix the problem by logging on and then attempting another upload of the same images I've already prepared for upload. Instead, I have to go to another page, logon, and then start the wizard procedure all over again from scratch. This is just not good enough - definitely a bug that needs to be fixed, and asap. Bahnfrend (talk) 13:57, 22 May 2015 (UTC)
Also from [[https://commons.wikimedia.org/w/index.php?title=Commons:Upload_Wizard_feedback&oldid=172414508#I_have_50_files_in_the_upload_stash_that_I_don.27t_seem_to_have_access_to_because_I.27ve_been_logged_out_during_the_last_stage_of_uploading | Upload Wizard feedback]]:
>I have 50 files in the upload stash that I don't seem to have access to because I've been logged out during the last stage of uploading. I had everything done up to the very last "publish" stage, at which point I encountered the "You must be logged in to save files in the upload stash." failure message for my first three files in the stash, and then nothing (except the "Remove" option) for the other 47 files. Like I said, everything is in the system (the files, descriptions, categories, geocodes, etc.), so this should simply be a case of verifying that I'm logged in (which I am again now). Considering that, due to my slow upload speeds and thorough approach to describing uploads, I've invested almost four hours in this batch of 50 files, I really, really don't want to lose my work. […] Michael Barera (talk) 02:29, 18 September 2015 (UTC)