Process instances are getting cancelled Automatically

I think there is some more information needed here. For instance tell us about:

- What happens in the monitoring view of the processes?

- Does it happen to all processes?

- What do the system logs tell you?

- What has changed that may have caused this?

1)i checked the flow process was stopped in user input task node .in the monitoring mode its showing as cancelled

2)No its not happening to all process .but it happened almost all the places where ever we used user input task  task is not assigned to the user but its cancelled

3) Yet to check the sys logs

4)Nothing we changed its happening in the prod environment 

1)i checked the flow process was stopped in user input task node .in the monitoring mode its showing as cancelled

2)No its not happening to all process .but it happened almost all the places where ever we used user input task  task is not assigned to the user but its cancelled

3) Yet to check the sys logs

4)Nothing we changed its happening in the prod environment 

Appian does not cancel processes by itself and data management has nothing to do with it.

Could it be that someone decided to cancel "old" processes?