Log-in loops are usually caused by your browser not having 3rd party cookies enabled or saving too much-cached data and confusing what information should be added where. Thankfully, this is a simple thing to fix on your browser. Please see the steps below on clearing cached data for your browser.
Enabling 3rd Party Cookies
Mac:
Safari: Unchecked Prevent Cross-site Tracking under Safari> Preferences> Privacy> Website Tracking.
Chrome: Go to Settings> Privacy and Security> Site Settings> Cookies and Data> make sure "Block third-party cookies and site data" is not checked.
Firefox: Set FireFox to Remember History Under Firefox> Preferences> Privacy> Choose Remember History.
PC:
Chrome: Go to Settings> Privacy and Security> Site Settings> Cookies and Data> make sure "Block third-party cookies and site data" is not checked.
Firefox: Choose Menu> Options> Privacy and Security> Choose Remember History under History.
Microsoft Edge: Go to Menu> Settings> Privacy and Security> Choose Don't Block Cookies under Cookies.
Clearing Cache
Note: For best results, clear basic cache for as far back as possible.
Mac:
Safari: Clearing Your Safari History
Chrome: Clearing Your Chrome History
Firefox: Clearing Your Firefox History
PC:
Chrome: Clearing Your Chrome History
Firefox: Clearing Your Firefox History
Microsoft Edge: Clearing Your Microsoft Edge History
Other Notes:
Restart your computer after making changes for the best results.
Be sure that your browser is fully up to date. This is particularly important if you are using Safari as your main browser.
Be sure your device doesn't need any operating system updates.