Enabling APO blocks admin-ajax.php

Howdy folks,

My platform.
Latest Wordpress on CyberPanel, using OpenLightSpeed. I use LS Cache plugin.

I just purchased APO. When I enable it, my wordpress theme search engine stops working. Console says “Failed to load resource: https://mydomain.com/wp-admin/admin-ajax.php?post_title=sakshi&action=rz_dynamic_explore, the server responded with a status of 400 ()

So far what I have done:
Disabled all plugins except for what is required with the theme.
Disabled all the options in CF Dashboard. Except APO.
Cleared my browser and also used Private Mode.
Created bypass rules in CF to bypass admin-ajax.php

When I disable APO. Everything works fine. When I enable it. I end with the above error.

Any advice??

Cheers

HD