When calling a web service (rest or soap) Stambia is creating a temporary xml file that will store the invocation and the response data. This file is then used as a source for the load template.

The temporary xml file is by default created in the runtime's temp directory and its name is metadata id. 

You can check the file name by viewing the "IN_FILE_NAME" of the action that calls the webservice in the template :

This creates a problem when we have a WebService call in a mapping that can be executed multiple time simultaneously because all the executions by default will try to use the same temporary file.

To solve the issue use the "Out File Name" option on the Integration template and make sure that the name of the file is unique ideally by adding a ${/CORE_SESSION_ID}$ variable into the path which will make the file unique per session.

Please note that the same configuration must be applied in "In File Name" of the "Load Template" that follows the call.

Other than that make sure to explicitily delete the temporary file at the end of your process otherwise after a couple of days you might find youself with a lot of temporary files on your machine: