Characters appear as � following change to PHP 5.6 or higher

Symptoms

You may see characters appear as � following after changing the PHP version for the site from PHP 5.5 or lower to PHP 5.6 or higher.

Description 

This can be caused by the default_charset being changed to UTF-8 in PHP 5.6. This change is noted in the following documentation.

https://www.php.net/manual/en/migration56.new-features.php

Workaround

You may be able to resolve this by adding the following to your site's PHP ini file.

default_charset = ""