Here's the script from HICC to correct your data:

-- Setting this variable to 1 will set the new end date to all cases that have a status of closed (either directly or through custom case states). Default: 0

DECLARE @PerformUpdate BIT = 0

-- Setting this to a valid date (YYYY-MM-DD) will set the case closures to to indicated value when PerformUpdate is 1. Default: '2025-12-03'

DECLARE @NewEndDate DATE = '2025-12-03'

-- Setting this to 0 will include all cases in the SELECT statement (does not affect the UPDATE statement). Default: 1

DECLARE @ShowOnlyMissingEndDate BIT = 1

-- Setting this to 1 will call a second SELECT query in the execution that reveals the number of cases that need a new end date set. Default: 0

-- This count should be 0 after running this script with PerformUpdate = 1.

DECLARE @ShowCaseCountNeedingUpdate BIT = 0

IF @PerformUpdate = 1

BEGIN
UPDATE c
SET c.DateCaseClosed = @NewEndDate
FROM HIFIS_Cases c
JOIN HIFIS_CaseStateTypes cst ON cst.ID = c.CaseStateTypeID
WHERE (c.CaseStateTypeID IN (2,3) OR (cst.RollUpID IS NOT NULL AND cst.RollUpID IN (2,3)))
AND c.DateCaseClosed IS NULL
END

SELECT CaseID, CaseState, RollupCaseState, DateCaseOpened, DateCaseClosed, NeedsEndDateYN
FROM (
SELECT c.CaseID, c.CaseStateTypeID, cst.NameE CaseState, cst.RollUpID, rollupState.NameE RollupCaseState, c.DateCaseOpened, c.DateCaseClosed,
CASE WHEN (c.CaseStateTypeID IN (2,3) OR (cst.RollUpID IS NOT NULL AND cst.RollUpID IN (2,3)))
AND c.DateCaseClosed IS NULL THEN 'Y' ELSE 'N' END AS NeedsEndDateYN
FROM HIFIS_Cases c
JOIN HIFIS_CaseStateTypes cst ON cst.ID = c.CaseStateTypeID
LEFT JOIN HIFIS_CaseStateTypes rollupState ON rollupState.ID = cst.RollUpID
) cases
WHERE (@ShowOnlyMissingEndDate = 1 AND NeedsEndDateYN = 'Y')
OR @ShowOnlyMissingEndDate = 0;

IF @ShowCaseCountNeedingUpdate = 1

BEGIN
SELECT COUNT(*) CasesNeedingUpdate
FROM HIFIS_Cases c
JOIN HIFIS_CaseStateTypes cst ON cst.ID = c.CaseStateTypeID
WHERE (c.CaseStateTypeID IN (2,3) OR (cst.RollUpID IS NOT NULL AND cst.RollUpID IN (2,3)))
AND c.DateCaseClosed IS NULL
END

Fixed in 4.0.61.1

Note that this affects activity/inactivity, so if you're finding a lot of active clients that shouldn't be active, maybe this is why