Need details to diagnose the problem. adding another dimension to the chart shouldnt effect the total count for the year. so it must be a something in your data or expression or model. give examples, screenshot, something i can work with.
There is a dimension Business Segment connected with a link table
Link table has data for only 3 months for current year for Business Segment value "others", when I am adding Business segment dimension in chart the count of yearmonth is changing from 5 to 3 for Business segment "others"