IF statement unexpected result evaluation

Here's a clean PBIX: https://excelconsultingsolutions-my.sharepoint.com/:u:/g/personal/matt_excelconsulting_com_au/ETD-66G_A2NPmI3vgo2tr1YB8camYrglTp4kKVxZ5A65zQ?e=BRaWtu

In the matrix you'll see the measure [Opp] which is the culprit:

Opp = IF([Opportunity]>=0,[Opportunity],0)

I have used variables to create [Opp MATT] which works as expected.  I'm not familiar with all the business logic and this is not my creation.  Am only interested in being able to explain why the conditional test then produces what looks like a different result.