I think I accidentally flagged an article reading on my phone. At least it turned gray and disappeared. I doubt a lot of permanent harm came from this but I tried to find a way to un-flag it and found nothing.
Would this make sense for a feature?
Workaround: Hiding an article only hides it from the article list, but you can still go to it if you have the URL. Then you can click ‘unhide’ or ‘unflag’. To find the URL, what I usually do is browse lobste.rs logged out (e.g. in an incognito window or another browser), find the article there, then copy/paste the URL to my logged-in browser.