Win 10 Task Scheduler randomly running tasks at non scheduled times

Question

I have 3 computers logged into a Windows domain (at home), and each runs a Scheduled task once at 3:05 am every third Friday morning. The job runs an image backup of the machine's C: drive. The three machines are staggered, so an image backup is run every Friday, each machine running every 3rd Friday.

This all works great except, every once in a while one of the machines runs on a Friday for which they have NOT been scheduled. I get 2 machines running on these days. The schedules all look correct - that is, each machine's schedule remains correct, but for some reason a task is run when it is not scheduled. What I mean is that the date for the "Next Run Time" is unchanged.

For example, say a task runs on Friday July 8. After that task runs, "Last Run Time" is set to "7/8/2022 3:05 am" and "Next Run Time" shows as "7/29/2022 3:05 am". But the task may then run an extra time on 7/22, after which "Last Run Time" is "7/22/2022 3:05 am" and "Next Run Time" is "7/29/2022 3:05 am".

No idea why the extra task is run on 7/22. This happens maybe once or twice per month, and when it happens, it cycles through the 3 machines. That is, machine A will run the extra task, then the next time it happens, it will be machine B (or machine C); the next time will be machine C (or B).

The fact that the extra run is staggered leads me to believe that this is a problem in Task Scheduler.

I have attached an image of the task trigger dialog to show the settings I'm using.

Any help would be appreciated.

Answer 1

Have a look at these posts.

https://learn.microsoft.com/en-us/answers/questions/439237/task-scheduler-server-2019-runs-tasks-every-week-i.html

https://learn.microsoft.com/en-us/answers/questions/724262/task-scheduler-jobs-in-windows-server-2022-and-ser.html

I believe that the solution for you is to set the task run every 21 days.