Getting ridiculously wrong subtotals in matrix visual

[Dave_Gugg]

I am trying to build a visual with three rows and no columns.  When I add a couple of values that I am bringing in from a data set, the subtotals are either correct for one or the other, not both:

Above, Net Shipped Units subtotal correctly

Above, Net Shipped Dollars subtotal correctly.

It appears whichever column I add latest has the correct subtotal.  Both of these metrics are coming straight from my fact table - there are no calculations done on them from inside of Power BI, aside from the option to sum them within the matrix visual.

However, I next try to add a custom metric, and now I get a number that is even more wrong than 0:

The calculation for the custom metric is pretty basic:

Net Ship GM% = DIVIDE(SUM(Demand[Ship $]) - SUM(Demand[COGS]),sum(Demand[Net Ship $])) 

What am I doing that is causing these subtotals to aggregate incorrectly?

Thank you