The activity log is useful to pin point who brought changes to the schedule.
You will find it under the More button -> Activity log
Once you are in the Activity Log, you will know who changed what and when. You will be able to analyze these types of changes :
Creation of shifts
Modifications
Copies
Transfers
Publishes
Deleted shifts
It is also possible to only filter changes by Manager and/or for a specific date. See the following example :
