Hi, @plusnethelp (Anoush) on Twitter requested I pass this on here.
The 'password reset' email for the Community is a multipart/alternative MIME email containing text/plain and text/html alternatives. Both have the same URL to open to reset the password. It ends in '..', i.e. two full stops. This works fine in the text/html as it's delimited by the HTML mark-up. It has a high risk of failure in the text/plain as terminals that spot and allow a URL to be opened or selected assume trailing punctuation is part of the surrounding text, as it often is, and thus open the reset URL without the '..'.
The page opens, it looks correct, I fill in the form and submit, and the new page loads with an error saying to fix the highlighted problems, there are no highlighted problems, and I'm back where I started. I obtained several 'reset password' emails and the URLs always ended with '..'.
To fix, make clear with additional text in the email that the dots are part of the URL, or better still remove them, or append something so they're not the last thing, e.g. '#'.