Why is the "Not Recovered" total in the Dunning Effectiveness report and the "Non-Payment" total in the Churn Analysis report not matching up?

In a nutshell, these two metrics are not expected to match up. 

The difference is related to the dates used to calculate the two metrics. Churn is representative of when subscriptions actually ended while dunning is tracking the end result of the invoices that were created in a given time range. Therefore, the Non-Payment metric in the Churn Analysis report uses the date that the subscription expired whereas the Not Recovered metric in the Dunning Effectiveness report uses the date that the invoice was created/posted.