For what it’s worth, I had a particular post that was being stubborn and giving me the 404 error each time I saved it, and was able to glean a little info from seeding the ‘post.php’ file with a few ‘error_log’ statements and seeing what popped up in the php error log.
The problem seems to result from the ‘$location’ for redirection in post.php being set incorrectly (duh). In this case, the path being taken through the post.php file went through the ‘editpost’ action/case, and $location was set by the
elseif (isset($_POST['referredby']) && $_POST['referredby'] != $_SERVER['HTTP_REFERER'])
{
$location = $_POST['referredby'];
lines in that case (line 113-114). The location was NOT then altered by the following if statement and get_permalink () call.
You can’t tell this from the resulting address in the browser after the failure, but the entire $location seems to be set to:
<div id='error'> <p class='wpdberror'><strong>WordPress database error:</strong> [You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near ') ORDER BY post_id, meta_key' at line 1] <code>SELECT post_id, meta_key, meta_value FROM wp_postmeta WHERE post_id IN() ORDER BY post_id, meta_key</code>
</div>https://www.whateveryourblogis.com/wp-admin/post.php
That’s the only info I’ve gotten so far – it would seem that the problem, at least in this case, was tied to that line of $location = $_POST['referredby'] on line 114 of post.php.
At least that’s what my simple debug would indicate. I’m not sure where that error info comes from, or if ‘referredby’ just happens to be garbage at that point. Maybe that info from the incorrect $location will ring a bell with somebody.
