Issues with admin-ajax.php

Guys, I have a serious problem 🙁
Occasionally when I enter http://mywebsite.com/wp-admin/admin-ajax.php I see Page not found, instead 0. Now, on the posts kojipostoje occasionally reports an error type Page not found. In 404 Monitor I see URL with 404 Error http://mywebsite.com/wp-admin/admin-ajax.php.
I hope to find a solution.
Any help is welcome