FinApHoldApproval not respecting "Don't send multiple notifications for the same human task event"

Summary:

We have implemented FinApHoldApproval to send notification to requesters in case of invoice is placed on receipt hold. we have also checked "Don't send multiple notifications for the same human task event" in BPM so as to avoid sending multiple notification for the same Invoice.

However, even after checking "Don't send multiple notifications for the same human task event", system is still sending multiple notifications for multiple lines that are on hold.

I am sure to have achieved this requirement in past, am I missing anything apart from this check box?

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