At this point, if you try to login in the Drupal 8 website you will be rejected, it’s because the login system doesn’t read directly the table users_field_data instead of a cache for entities is used.
To flush the cache for a specific user entity with compromise the rest of cache of your system you can use the following SQL statement.
DELETE FROM cache_entity WHERE cid = ‘values:user:1’;
Now you can grab a cup of coffee/tea and enjoy your Drupal 8 website.
Hope this will help you.