Duplicate Survey records created even when 'Prevent Duplicates' option is configured
In rare circumstances, you observe duplicate Survey records even though the 'Prevent Duplicates' option is configured. The Survey records have created date/time plus or minus 1 minute.
The first step in preventing duplicates is to verify the 'Prevent Duplicates' option is configured. If it is not, you should configure it per the following documentation: Preventing Duplicates
If a survey recipient opens multiple links from the survey at the nearly the same time, the Simple Survey page can load multiple times before each survey record is committed to the database. The query used to identify duplicates therefore returns no results so duplicate records get created. Each transaction on the Salesforce platform is atomic and Salesforce does not provide a mechanism to synchronize data between execution threads. This is a limitation of the Salesforce platform.
This is a limitation of the Salesforce platform.