By analyzing schedreport.txt you can find out name and SID of the user who scheduled and ran the task, as well as the name and time and date of when the task was executed.
Sample of a successfully executed task
Utility that allows you to manage scheduled tasks and collect reports in Acronis products
AcronisInfo is a utility that automatically gathers User Rights Assignment list, Windows Event Log, Msinfo32, Acronis registry keys, Acronis logs, Acronis Scheduler report, Acronis Disks Report and list of user’s Active Directory groups
Update Acronis Scheduler and recreate the tasks