This behavior of freezing (i.e., Outlook stops responding for a while) when you navigate or click the Team Helpdesk Ongoing Cases, happens if any of the monitored email folders or mailboxes are invalid. In other words, one or more path of the monitored folders or mailboxes have changed or unavailable. Due to this, Outlook takes some time to scan through the Outlook folders hierarchy (in case of email folders) or Exchange stores (in case of mailboxes).
To fix this freezing state, go to Team Helpdesk Manager > Settings > Email Monitoring. And under Email Monitoring settings panel, verify each of the monitored folder/mailbox are valid, and that the path are correct. If there is any discrepancies, remove the entry from the monitored list, and if required, add the correct folder/mailbox. Save the changes. And restart Outlook, and the problem with freezing should go away.