https://commons.wikimedia.org/wiki/Commons:Upload_Wizard_feedback says to report this here.

I'm using a tiny cell phone. So bear with me. The template won't fit.

Here we see one of the files has failed to upload. The only choice is to remove it. Even though in the words it says try again, but there is no try again button. Therefore the user must painstakingly remove it and then dig in his files and add it back in. Simply adding a try again button would avoid all that trauma.