I have created a workflow that copies items from one list on one site collection to another list on another site collection. When the workflow is started manually, it runs fine without any issue or error. 

However, when the workflow is executed via schedule, it always fails with the following error message: "An error has occurred in (Workflow Name)".

So far I was not able to find the reason for the crash. And I also do not understand why it only happens when the WF is scheduled. Does anyone have any idea what is going wrong here?

Thank you.