Issue while creating analysis using Max and Avg functions in new calculated measure.

Summary:

We are trying to create a analysis for sales order processing lead time, but we are facing issue as the new calculated measure using avg function is not giving correct expected values.

Content (required):

For the order processing lead time analysis, we are comparing the order creation date and invoice dates and then taking the time in between these two to arrive at the order processing lead time. However, as there are multiple invoices for a same sales order, we used "Max" function on the invoice date attribute to get the latest invoice date for a particular sales order. Then we created a new calculated measure and took the avg of difference of max of invoice date and the creation date to get avg lead time over a given time period. however, the result