Hi!
I have no knowledge of PHP 5.5 issues with the current plugin version. I’m running this server (as well as the demo) on php 5.5 and it works fine: https://wp-dreams.com/phpinf.php
If you are using an older version of the plugin (3.5<) I would recommend updating the plugin - don't forget to check the update notes in the documentation. Are there any specific error messages related to the issue?