Duplicate Sample Limit Transactions are created when Calls error on sync which causes the Sample Limit to be incorrect.
If a Call errors while syncing Online, Sample Limit Transactions can be created to prevent any data loss.
A common cause can be a validation rule that did not error Offline but is erroring Online, preventing the Call from being submitted.
Correct all errors affecting the Call.
Delete the duplicate Sample Limit Transactions. Update the Sample Limit or make a manual adjustment to the Sample Limit.
CRM Knowledge Article: CRM Error Reference Guide