Forum has been updated last night to the latest and greatest phpbb. As a result some older browsers are no longer supported and will not let you login for security reasons. If you're on a mobile and cant login you may need to update or upgrade your browser.
My ancient duckduckgo browser from years prior no longer works on my andriod mobile.
Also, someone mentioned they had to clear their cookies as well.
Another thing that was changed was remember me logins. If you use autologin you will now be asked to enter your password in once a year.