First, I'd like to point out that, what you used in the workbook for the two data sources is not join, but data blending.
Reference: Blend Your Data
The result looks correct under the use of data blending.
Take "Account ID" 1 for example,
In data source "Initial", there are three initials for it, c,a b;
In data source "Main", there four rows for it, the sum of which is 5,770,900.
So could you specify what is your expected result?