It seems like it might be the plugin. I have disabled it and enabled paypal and I have not received any issues.
Yeah, this issue has happened to me too.
`PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, class ‘NM_PersonalizedProduct’ does not have a method ‘ppom_files_removed_unused_images’ in /home/…/public_html/staging/wp-includes/class-wp-hook.php on line 286
