This is because of your security permissions. The Security screen is where you (Owner or Admin) can control access or grant permissions to you (logged-in user) to various screens as well as the individual reports. You can edit or customize the security permissions by opening the Security screen from Settings > Access & Permissions. Go to the Reports module in the list to see the permissions. For the individual reports, go to the Reports tab and check the relevant permissions for the reports. Check CORE Help Center for details.