The issue is mainly resolved. It was my own account with one of my other email addresses. I forgot that I have an account with that email address. Still an issue: the website will not allow me to logout and login with a different account. To do so, you need to clear the browser’s site data.
When I press the login button in this forum, the page will immediately log me in without me entering any credentials. What’s more, the user it logs me in as (crikot), is unknown to me. I am not crikot.
I would like to be able to login with my own user account. Please help.