System Operators have access to view specific listing of cancellations. Go to the Schedule page, find the 'View' pull down selector and find either; List by ID_NO, include Cancelled or List by Date, include Cancelled. See image below for selection of 'View'. After selecting the view, click the button for refreshing the schedule.
You have the option to filter this selection by date, resource, location and even by user, if you suspect a culprit. The schedule listing will show all schedules for the period selected. Any that have cancellations will be highlighted in Magenta. See image below for a screen shot. Notice that the Made/Info column has information about the user and time that the schedule was made and/or cancelled. The user will only be listed if it is different than the user scheduled. In the example below, the schedules for 'Heidi Haverlock' were all made by Heidi. Therefore, the user is not listed. On the other hand, the cancelled schedule for Mary Billing was made and cancelled by 'Heidi Haverlock' user 30639, so it shows that information in the Made/Info column.