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 = ""