I could see very quickly why there is an issue.
This filter in the table is doing nothing
Because it sits here within your model. With how your relationships are setup there is no way for any filter to reach across to the calculations that are in the table
You’ll see I take that out of the table and nothing changes from the results
Because of the model, the formula is really worthless and needs to be improved.
Certainly review this course if you can. Filter needs to flow from the top layer down (think waterfall).
This is the formula you need. Well this gets a answer, may or might not be right, depends how you want to show this.
Bias Measure (New) =
IF( HASONEVALUE( Date_Dimension[MonthYear] ),
DIVIDE( [Total Sales Quantity], [Historical Forecast Units], 0),
AVERAGEX( SUMMARIZE( Date_Dimension, Date_Dimension[MonthYear],
"Grouped Bias", [Bias Calculation]),
[Grouped Bias]))
Also couple of other tips having seen the model. Really look to format formula if you can. Helps immensely in understanding how formulas work.
Mainly the model. Getting the model setup with simplify things immensely here.
Chrs
Sam