Check the following

1. Settings for the calendar to make sure that Free/Busy times are visible
2. Verify that the events are published and that they do not have any restrictions such as passwords or blocked domains that may be preventing them from appearing
3. Check any other clients that are linked to the Microsoft calendar like Outlook to make sure that they are not overriding what is being shown
4. Ensure that the calendar itself is not locked and that sharing privileges for it are enabled in the Microsoft account settings