I shifted to new host recently and I didn’t realize a lot of my pages were down and showing this error message. Then gradually I found out that the problem is with my bank category and pages that are under bank category. This are “custom post” considering wordpress term. They were called item in my wordpress theme that I’m using. It’s directory theme from Ait-Themes.
The fix was simple, after several correspondence with my new host they said the fixed the problem by increasing MEMORY_LIMIT to 256MB for the websites to work. Just in case you don’t know where MEMORY_LIMIT is it’s in php.ini . But that is not the only place where you can change and they didn’t change from there. Rather they changed it in wp-includes/default-constants.php . I still don’t know why! and how is it different.