Lambda triggered twice by one dynamodb insert event

I have a lambda function which is triggered by Dynamo stream when a record is inserted into a table. The function takes about 2~3 minutes to process the request and the batch size for the trigger is configured to be 1.

For some reason, the lambda function is triggered twice for every record inserted into a table. For instance, I inserted 100 records into the table and found out that the lambda function was triggered 200 times.

Below is the screenshot from CloudWatch which shows the lambda function is triggered twice for the same pk inserted into the dynamodb table.