Measure not working when selected multiple months

AshP , Try to use time intelligence functions

examples

MTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESMTD('Date'[Date]))
last MTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESMTD(dateadd('Date'[Date],-1,MONTH)))
last month Sales = CALCULATE(SUM(Sales[Sales Amount]),previousmonth('Date'[Date]))
MTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESMTD('Date'[Date]))
last MTD Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESMTD(dateadd('Date'[Date],-1,MONTH)))
last month Sales = CALCULATE(SUM(Sales[Sales Amount]),previousmonth('Date'[Date]))
next month Sales = CALCULATE(SUM(Sales[Sales Amount]),nextmonth('Date'[Date]))
this month = CALCULATE(SUM(Sales[Sales Amount]),DATESMTD(ENDOFMONTH('Date'[Date])))
last MTD (complete) Sales = CALCULATE(SUM(Sales[Sales Amount]),DATESMTD(ENDOFMONTH(dateadd('Date'[Date],-1,MONTH))))

Power BI — Month on Month with or Without Time Intelligence
https://medium.com/@amitchandak.1978/power-bi-mtd-questions-time-intelligence-3-5-64b0b4a4090e
https://www.youtube.com/watch?v=6LUBbvcxtKA