It's understandable that having an NDA prevents sharing a packaged flow, but unfortunately there's just not enough detail here to know how to offer a direction. The design time flow execution can be slightly different than batch-mode (running the flow to output) execution and might result in something different if an order of operations is slightly different. Have you tried doing the calculation anywhere else in the flow?
If you are still having the issue, please share as much as possible (screenshots, definitely the calculation code, and whatever else you can).
I second Joshua - we'd need more detail to investigate the issue you are running into.
Also, a note about the data you see as you build out the flow - it could be that your data is Sampled. You can see that if there's a Sampled badge as below in the profile header:
That said, when you run the flow in batch-mode to create the output datasource, Prep bundles all the transformations and runs them efficiently against all your data. So the first few rows you are looking at in Prep could be different from the first few rows you see in the datasource you connect to in Desktop.
Can you verify that the calc isn't being computed correctly for the exact same data row? For instance looking at a particular effort_id and end_time?
Senior Product Manager