Comments disappearing

The old comments on my blog disappeared and new ones won’t post. How do I fix this? I tried deactivating all plug-ins but this did not fix the problem. The website is https://www.thefitscoop.com Also, when you try to leave a comment the following error message appears: Warning: get_object_vars() expects parameter 1 to be object, null given in /home/andmer12/thefitscoop.com/wp-includes/comment.php on line 171