How is the third party scheduler actually calling the Informatica jobs? thru the API or runAJob CLI?
This looks to be an issue at the D series scheduling tool that you are using. You might have to look at the configurations in this tool to understand if there is any hard limit that is being used after which the job shows as completed.
If tasks are finishing successfully in Informatica then the issue is with D-series scheduling tool. It must have some Configuration setting that is releasing the control and completing the tasks in 40 mins.
Please validate the status of the Task once it finished in D-series. See if they are exiting due to time-out.
This issue is seen when the job status is not getting updated by the server in Informatica cloud.
Run the tasks without the scheduler and check how much time is it taking to update the status of the job.
Verify the tomcat.log for that run instance if there is any stats returned .
Also please confirm if you are using runajobCLI utility to trigger it in the scheduler.