Power BI DAX function

Hi Anonymous -I have modify the code slightly. The issue might arise from how LWK or CWK variables using the coalese function there to handle blanks. 

Demand =
VAR _startdate = MAX('MDS Report'[MDS Date])

VAR LWK = CALCULATE(
SUM('MDS Report'[Quantity]),
'MDS Report'[WK] = "LWK",
'MDS Report'[Week] >= _startdate,
'MDS Report'[Week] <= _startdate + 91
)
VAR CWK = CALCULATE(
SUM('MDS Report'[Quantity]),
'MDS Report'[WK] = "CWK",
'MDS Report'[Week] >= _startdate,
'MDS Report'[Week] <= _startdate + 91
)

-- Ensure LWK and CWK return 0 if they are BLANK
VAR LWK_Valid = COALESCE(LWK, 0)
VAR CWK_Valid = COALESCE(CWK, 0)

VAR Change = SWITCH(
TRUE(),
LWK_Valid = CWK_Valid, 0,
LWK_Valid = 0 && CWK_Valid <> 0, 100,
CWK_Valid = 0 && LWK_Valid <> 0, -100,
LWK_Valid <> 0, DIVIDE((CWK_Valid - LWK_Valid), LWK_Valid, 0) * 100
)

VAR _total =
IF(ISBLANK(MAX('MDS Report'[Month])), 0,
IF(DISTINCTCOUNT('MDS Report'[Month]) > 1,
FORMAT(Change, "0.00") & " %",
FORMAT(SUM('MDS Report'[Quantity]), "")
)
)

RETURN COALESCE(_total, 0)

Hope it works, please check