Problem-: I have setup workflow rule to send out auto message. I am doing mass update by uploading a file, which update fields on which workflow is setup.
Workflow rule is triggered, task is also created but nothing happens after that. There is no SMS record created in SMS History.
When you were doing file upload, it was performing field update in a batch. With that batch execution, workflow rule was trigger and was creating tasks.
With our "SMS On Workflow" addon, whenever a task (with specific configuration Id mentioned in comment section) is created, a trigger is invoked which in turn was invoking a @future method to send out messages in your case.
Salesforce does not allow @future method to be invoked from batch. As a result of this Salesforce limitation, SMS is not sent and SMS history record is not created.
Solution to this problem is instead of creating task as an immediate action, create task as a scheduled action. This will ensure that the task is created outside a batch context and therefore @future method invocation is possible.