I am using the transition_post_status to process a post being published. However, on one of my test installations, this is not being called the same as another installation. I have tracked this down to the AJAX calls being made from the post compose page itself.

These are the requests being made when I transition a post from a draft to published on my two installations:

As you can see, the AJAX call to post.php is not being made in the second example. It turns out that the global $post object is in a different state inside transition_post_status hook when being called via post.php, which is why my code only works on the first installation.

Both installations are running 5.7.2, and are stock aside from the 1 plugin that I am working on, which is the same on both installations.

Can anyone shed any light on why two different installations are triggering different AJAX calls when publishing a post?