Scenario:
Multiple users find a particular report missing or the settings of the report has changed.

Cause:
This usually happens when an Administrator has deleted the report or modified it in his account.
When an administrator modifies a report or makes any changes to a report, then it will affect the report only on his account. However, if the changes are made from the manage report page then it will affect the report globally, hence affecting all the users who have access to the report.

Note:
Users can change the settings to their requirement by changing the settings on the report, at their end, provided they have the option to do so on the report.
If the same report is deleted by the administrator then the report will disappear from the list of reports, then no user within the system will be able to access it.