There are 2 aggregations.

When you create any measure in the rpd you specify its aggregation.

Independent of this there is also the aggregation of what answers should do as an aggregation when you add a total specifically to a report field, or to an area in a presentation or similar.

It does not always make sense for the two aggregations to be the same, and sometimes you will want to / need to override the defaulted aggregation on an answers based aggregation.

In your case summing month to date will produce a spurious result, as the last month is the sum of all proceeding months.

On that basis I might suggest that the best suggestion for that column is not to have a total.

Out of interest what number does 'Server Complex Aggregate' produce?