When you change the IP, apache will serve up the generic success page for the URL unless it is coming from the new
IP. That is, if the old IP is 188.8.131.52 and you change the site to 184.108.40.206, your local DNS cache will still be trying 220.127.116.11 for a while and so you will see the generic page.
There are two solutions - the easiest is just to wait.
The more complex, but immediate, solution is to jump into the httpd.conf file, if you can't wait, and add the second IP in the virtual container for that domain. That is, this:
<VirtualHost 18.104.22.168 22.214.171.124>
(Obviously you find and change just the VirtualHost line enclosing the section for that domain only.)