By default Service Grid in Icinga Web UI is limited to 20 services and 20 hosts.
You can change those limits by altering following:

grep -e \'[xy]\'\,\ \'limit /usr/share/php/Icinga/Data/PivotTable.php
$limit = $this->getPaginationParameter('x', 'limit', 100);
$limit = $this->getPaginationParameter('y', 'limit', 100);