I think, it’s because of DNS problem.
The old site URL is likely the public DNS name for your EC2 instance when you installed WordPress.
If you are not sure of your old site URL, you can use curl to find it with the following command.
curl localhost | grep wp-content
You should see references to your old public DNS name in the output, which will look like this (old site URL in red):
<script type="text/javascript" src="http://ec2-52-8-139-223.us-west-1.compute.amazonaws.com/wp-content/themes/twentyfifteen/js/functions.js?ver=20150330"></script>
Download the wp-cli with the following command.
curl -O https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
Search and replace the old site URL in your WordPress installation with the following command. Substitute the old and new site URLs for your EC2 instance and the path to your WordPress installation (usually /var/www/html or /var/www/html/blog).
php wp-cli.phar search-replace 'old_site_url' 'new_site_url' --path=/path/to/wordpress/installation --skip-columns=guid
In a web browser, enter the new site URL of your WordPress blog to verify that the site is working properly again.
let me know if that works!