The Advanced Portal reports for Jira Service Management does not currently support Issue security levels. This means that even if you have set restrictions using the Issue security levels in Jira, the Advanced Portal reports will not take them into account when displaying the tickets in the report.
In general, issue security levels were introduced in Jira, long before Jira Service Management was created. Their idea is to restrict issues for the Jira users and trying to use them in the JSM portal to restrict standard customers is not their intended purpose. Similar effect can be achieved by not setting Customer Request Type for those issues that should not appear on the JSM Portal.
Our team currently investigates how the app can take into account the Issue security levels, so if you need this, please raise a ticket in our Support center and we will let you know once it is fixed.