When on /login/index.php if the MoodleSession token is made invalid
An infinite loop will occur where the site attempts to refresh to reattempt signin.
However, it does not reset the MoodleSession token, hence it just loops.
The only user rectification for this is to clear cookies.
To recreate this,
Goto /login/index.php eg: https://moodle2.richuish.ac.uk/login/index.php
Then open console and type document.cookie="MoodleSession=gibberish"
Upon refresh, the described loop will occur.