Hmm - blocked cookies will let you login, but unblocking cookies does not? I'll check in to this. We do require certain cookies to have the site work correctly and remember you from page to page.
It's possible it may have picked up a bad cookie somewhere along the way (like a raisin oatmeal

). Have you tried clearing them and starting fresh?
On Safari, to clear just this site:
On desktop - Preferences >> Privacy >> Manage Website Data >> search for "hellcat" and hit "Remove" on what comes up. ("Remove all" will clear all of your history data)
On mobile - Settings >> Safari >> Advanced >> Website Data >> search for "hellcat" and remove what comes up
If you save your login to your browser, trying deleting that and manually entering the information. Sometimes funny things happen there, too.
And of course, be sure it does select "Remember Me" for you.