SharePoint Online Designer 2013 workflow, terminated on autostart

Question

In SharePoint Online, I have a SharePoint Designer 2013 List workflow. The workflow can be started manually without any problems (I am starting it on a custom Documentset content type called "ServiceOrder").

When I set the workflow to start automatically when a "ServiceOrder" content-type item is created. The workflow terminates instantly.

Details: The values provided for the root activity's arguments did not satisfy the root 
activity's requirements: 'DynamicActivity': Expected an input parameter value of type 
'System.String' for parameter named 'UniqueId'. Parameter name: rootArgumentValues

I have created another simple workflow just to check if's able to start automatically, and the new simple workflow does start automatically.

Answer 1

Finally I understood what the error was. I have created a variable named "UniqueId", which represents the items UniqueId (Guid). I'm using this variable in a REST call to "GetFolderById".

After I changed that variable name to UniqueGUID, everything worked. Seemed like a reserved variablename needed to initiate some Azure automation etc.