Consider the following scenario:
You're using a Collect Feedback – SharePoint 2010 workflow in SharePoint Online or SharePoint Server.
The tasks list where the feedback items are tracked for the workflow has a column or columns for which the Enforce unique values option is set to Yes. For example, this may apply to the Start Date column.
You start the workflow and select multiple users in the Assign To field, and then you select All at once (parallel) for the Order setting.
In this scenario, the workflow doesn’t start the feedback process, and instead it reports a status of Failed on Start (retrying).
To work around this issue, do one of the following:
Select One at a time (serial) for the Order setting when you start the workflow.
Set the Enforce unique values setting to No for the affected tasks list column or columns in which the workflow tasks are stored.
When you start the workflow by using All at once (parallel) for the Order setting and when Enforce unique values is set to Yes, the workflow does not start because the values for the column aren't unique.
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