Do you get different results with/without the DISTINCT?

Here's a reformatted copy of the query. I've added table aliases to make it a little more readable and changed the order of the columns in the GROUP BY to see which ones are in the output list and which are not.

SELECT DISTINCT

h.RepairSheetNr,

v.unitnr,

v.groupid,

v.brandId,

v.modelId,

v.version,

v.Type_Fleet,

h.close_date,

-- you don't need this CASE because the condition already exists in a join: v.unitnr = h.UnitNr

-- count(CASE WHEN h.unitnr = v.unitnr THEN v.modelId ELSE 0 END) AS TotalModels

COUNT(v.modelId) AS TotalModels

FROM Vehicle v

INNER JOIN RepairSheetH h

ON v.unitnr = h.UnitNr

INNER JOIN RepairSheetL l

ON h.RepairSheetNr = l.RepairSheetNr

INNER JOIN CashFlow_Accounts cf

ON h.Company = cf.Company

AND l.cashflow = cf.CashFlow_AccID

WHERE l.cashflow = '201708'

AND v.Type_Fleet<>'FS'

GROUP BY

h.RepairSheetNr,

v.unitnr,

v.groupid,

v.brandId,

v.modelId,

v.version,

v.Type_Fleet,

h.close_date,

cf.CashFlow_AccID,

h.Date,

h.total_value,

l.cashflow,

h.UnitNr