Clearing out the cookies on the website.
To do so, click the site information button beside the URL bar then select "Cookies and Site Data". MAKE SURE YOU ARE ON THE WEBSITE THAT YOU ARE HAVING ISSUES LOGGING INTO.
Then "Manage on device site data"
Then just click the trash can for each one until there are no more trash cans to click.
Hit done
Refresh the page and try logging in again
If this doesn't work an advanced cache clear may be needed.