In my opinion, the messages are fraudulent about their intentions. They misrepresent a 'security-related' incident to get me to go on the site again.
Are you sure your internet profile elsewhere is not subjecting you to doxxing attempts? I know friends who are in publishing or blogging etc. with fairly well known profiles on the internet, and they seem to be targeted far more regularly with attempted unauthorised logins to their email and social media accounts.
I was contacted by an undergraduate asking for grad school advice. Five minutes later there were several emails in the inbox from Facebook with exactly that content. I don't normally receive anything at that address (everyone I know emails me at a different address). How do you expect me to give you advice when you pull this shit on me?