Getting Error 500 on Creating a New Index on Php 7.2 Maria DB

Hi i am getting an error 500 when i click on create new index :

Status: 500
Code: error

as of this i am unable to update my drafts or edit products as well

my error logs show this :
#4 /www/molbolo_793/public/wp-content/plugins/ajax-search-” while reading response header from upstream, client: 117.96.244.16, server: molbolo.in, request: “POST /wp-admin/post.php HTTP/1.0”, upstream: “fastcgi://unix:/var/run/php7.2-fpm-molbolo.sock:”, host: “molbolo.in”, referrer: “https://molbolo.in/wp-admin/post.php?post=1234&action=edit”

About My Config :
PHP Version 7.2.1-1+ubuntu16.04.1+deb.sury.org+1
MariaDB Server version 10.1.28-MariaDB-1~xenial
JSON Extension Your PHP install supports JSON.
MySQL utf8mb4 support Your MariaDB version supports utf8mb4
Communication with WordPress.org WordPress.org is reachable from your server.
HTTPS status You are accessing this website using HTTPS.
Secure communication Your WordPress install can communicate securely with other services.
Scheduled events No scheduled events have been missed.
Background updates
No version control systems were detected.
Your installation of WordPress doesn’t require FTP credentials to perform updates.
All of your WordPress files are writable.
Loopback request The loopback request to your site completed successfully.