Characters appear as � following change to PHP 5.6 or higher

Symptoms

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

Cause

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:

PHP: New features - Manual

Resolution

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

CONFIG_TEXT: default_charset = ""