Very strange.
works fine:
https://helloacm.com/?s=kasdjfaksjdf
but if any query containing “base64”, the page is empty
https://helloacm.com/?s=kasdjfaksjdfbase64
I have installed the latest WP version is 4.3 billie and I just CloudFlare.
not just one of the website, my other domain have the same thing:
Thanks for the suggestions.
I disabled the plugin one by one and find out it is the problem of “iThemes Security”
will raise this to their support.
https://wordpress.org/plugins/better-wp-security/
find out that unticking the following option in the plugin solves the problem
Filter Long URL Strings
Limits the number of characters that can be sent in the URL. Hackers often take advantage of long URLs to try to inject information into your database.