WP 404 on Saving Existing Posts (New Ones are Fine)

I'm migrating a bunch of sites at the moment and have found a weird error. I vaguely remember coming across something similar before but can't remember how I fixed it.

We have a site that has been cloned from server A to server B using managewp. On the new server if you try to save a post it returns a 404 error. We can add and save new posts without issue, so it's not a general issue with the posts.

Looking in the console in chrome it just shows:

POST httpx://www.my-cloned-site.co.uk/wp-admin/post.php 404

So far I have:

- Reset permalinks
- Checked the permissions of the post author
- Disabled all plug ins
- Tried with the default WP theme
- Checked the php version
- Checked the htaccess (it's just the default wordpress one)

Anyone come across this before or have any ideas?

Is it showing this somewhere in htaccess...

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress


It's related to permalinks, in case the permalinks reset didn't filter to htaccess. Long shot... but worth a quick check

It turned out to be ModSecurity. As soon as I disabled that it worked fine.

I'm still not sure why it affects old posts and not new ones though?