Currently sitemap is limited to show 500 entries. You can change it by editing your file located in /sys/app/controllers/indexController.php
search for line containing
$num_rest = 500 - count($links)
change it to
$num_rest = 5000 - count($links)
depending on how many ads you want to show.
Please note that if you use high value here your sitemap may load slow, become big and may not load at all, even crash your server so test that value with 1000,3000 then 5000. We do not recommend using more than 5000, approximately file size will be 1.3 MB.
In sitemap it is permitted to have 50.000 links but reading that many data from database on each age request is too much for a web server.
We will update our script to have 3000 links listed in sitemap.xml for the next release. Also add caching for 24 hours so that database is not loaded too much.