With no data or test script to work with, my guess would be that this part of the query
nashpats (7/22/2016)
(SELECT SUM(amount)
FROM dbo.vw_LT T2
WHERE T2.LinkID <= T1.LinkID
)Cumulative
Needs to be filtered in the same way as the main part of the query, so should read
(
SELECT SUM(amount)
FROM dbo.vw_LT T2
WHERE T2.LinkID <= T1.LinkID
AND t1.accnumber ='8400000'
AND t1.DDate BETWEEN '2016-04-01 00:00:00' AND '2016-04-30 00:00:00'
AND t1.DataSource = 'PAS11CEDCRE17'
)Cumulative