Cannot Log Into The Dashboard due to "Session Expiration" error

When logging into the Dashboard, if you are seeing this error:

You've been logged out.

This may be due to session expiration, private browsing, or disabled third-party cookies.

To continue, log in again or adjust your browser settings.

There are three possible causes and solutions:

Session Expiration

You have been inactively logged in for too long. The Dashboard has logged you out for security reasons.

Solution: Log in again to access the dashboard.

Private Browsing/Incognito Mode

Your browser is set to Private Browsing and is not allowing the Dashboard to store a session cookie.

Solution:

1) Disable Private Browsing, or

2) Enable Third-Party Cookies in Private Browsing/Incognito Mode - Click ⋮ then Settings, 'Privacy and security', 'Third-party cookies' then click 'Allow third-party cookies'

Third-Party Cookies

Your browser has disabled third-party cookies. 

Solution: Click ⋮ then Settings, then 'Privacy and security', and enable storage of third-party cookies.