Never had it happen with Groups.io, but have had it with other sites that require a periodic log-in. After several attempts to assure my self it was the site and not me, I gave up and created a new password. And every single time, upon further research, I had mis-typed the password. Either a mispelling, a missed capitalization or a missed special character. Or forgotten I had already changed the password. Not saying definitely that's what happened to you, but it's definitely a strong possibilty.?
Dave
