To troubleshoot issues with calendar reminders not working in Exchange, consider the following steps:

1. Check the Exchange Server for any log entries or errors.
2. Verify the Exchange server is reachable from the endpoint.
3. Verify the Outlook Client is working properly.
4. Verify the calendar reminders are enabled in the Outlook Client.
5. Check the Windows Event Viewer for any error messages.
6. Check the user’s mailbox for any permissions or restrictions.
7. Check the Exchange server storage limits.