I was working with an editor at an edit-a-thon (I assume her account was new) who was translating an article from enwp to frwp. But when she went to publish, the captcha overlay would not disappear nor were we able to move it (to see the options hidden behind the overlay). I hadn't worked with the tool before so I didn't know about the option to save her work to draftspace... perhaps that would have gone through? My hunch is that, as a new user, she lacked the permissions to write to frwp mainspace, but instead of the tool throwing an error with some explanation, it instead hung the captcha. (I wonder whether her progress automatically saved at https://en.wikipedia.org/wiki/Special:ContentTranslation)
Separate issue: She then attempted to backup her work by copy-pasting to an email, but of course she couldn't copy the references too and indeed wasn't able to select the entire column of translated text but had to copy each paragraph individually (a design choice perhaps worth revisiting?)
Anyway, not sure if this escalates to a bug-worthy report but wanted to give feedback here anyway. Feel free to reply if you think it would be helpful