If you have a scheduled jobset that is going to completed, then it could be because there is a restartable app engine in the job definition. To fix, find and restart the app engine that failed through the restart request option in process monitor. If the app engine is failing due to an error, you'll need to fix this first. Once it runs to success it will complete the job and also set the jobset status back to Active from Complete.
Scheduled Jobset going to Completed