New posts broken after transferring site to new host

Hello,

I’m having an issue with viewing new post after moving my site to a new host. I was hoping that someone might be able to help me with it? When previewing a new draft post I’m getting the following error.

Fatal error: Cannot declare class Single_Post_Template_Plugin, because the name is already in use in /home/noktalkc/public_html/hrh/wp-content/themes/gameaddict/gameaddict/post_templates.php on line 2

Wordpress is up to date, as is the theme. I’m also running php 7.1. The issue seems to only be affecting new posts. Pages appear to be fine.