If you sometimes use capital letters in your email address, try each variation of this as our login system is case-sensitive, e.g.
Issues with logging in or staying logged in may be a result of using the Google Chrome extension, Prolific Assistant. We recommend removing the extension by going to chrome://extensions/, and selecting 'Remove'.
Prolific Assistant, as well as other page monitors, are not developed by Prolific and as such we cannot guarantee that these will work with our site.
You can read more about these here: 503 Error page and page monitors