This may be more of a feature request than a bug (not sure which category it belongs in).
Users are sometimes confused when they get a mail from discourse, click on the link, land in a browser where they are not logged in to discourse, start browsing around, and then run into the “Looks like you’re enjoying the discussion” message - sample below:
Users get confused because they are being prompted to sign up - which then goes fubar because they obviously already have account (because they got here by following a user mail sent to them by discourse). Of course they could ignore this message if they had the presence of mind to remember that they must already have an account and just need to click the sign in link at the top right of the page…
Anyway - my suggestion is that this verbiage be changed to suggest signing in if you already have an account - or even better - maybe the links from discourse mails could include a query string parameter to clue the server in that this session represents a user that already has an account - and just needs to sign in - rather than prompting them to sign up.
On a related note - when a user signs in, is the session managed in a cookie? What is the maxlife of that cookie? is it “forever”?