While creating a matrix, I dragged "C_B_Date" in MTG table (highlighted in GREEN) to column and added two attributes in rows ("Drop or Active" in ALL_OD table & "Rolling_ttl_MTG" in MTG table, hilighted in BLUE)
In "Rolling_ttl_MTG", there are four values: Group 1,2,3,and 4
In "Drop or Active", there are two values: Active and Drop.
Thre relationships between tables are as the 1st. screenshot.
In the 2nd screenshot, even the summation of Group 1,2,3,and 4 are correct (i.e. equal to grand total), but the sum of sub-row values (Active and Drop) in each year are NOT equal to correponding Group 1,2,3,and 4 in each year. For example, in 2015, the number of active and drop added up far less than the number of group 1.