Recently we were getting the below error in one of our marketing forms for form submission record.
Exception in Creation of lead – Activity id: 40ff82fc-bb10-4d30-8671-12683392ccdf, Request id: AsChkx2zn5IKrjHVC4cTb6j-ZkB23D0PqgCdxwi8kEE_0, Exception: An item with the same key has already been added.
This was because we had mistakenly added first name fields twice as the form-matching attribute in the form-matching rule used for that form.
Deleting that extra field resolved the issue for us.
Hope it helps..
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