I didn’t see this until after I came back from the gym & so have not tried your version yet.
From my understanding, Intervals would not see the rest intervals without it saying “rest” specifically or using a metric of some value I think e.g. 0.1w.
But fundamentally I think that the issue is with the C2 FIT file anyway as the PM5 just behaves differnetly in terms of recording power/pace if it thinks that it is a rest interval. As explained here ( Concept2 RowErg FIT import ignores lap-defined work/rest intervals - #3 by Author_Bicep ) The FIT file just does not seem to contain a per second record for the rest interval, ot anything near per second even. So from what I am reading, however we parse ithe workout steps, rest Intervals will not show an accurate rest or “ticking over” interval by the look of it. It will register the passage of time at best, or seems to from my workout timeline graph, presumably from the time stamps, but without many data points recorded to register a lower/nil power.
My 2nd Feb 9:41 duration workout FIT (but actually 20:00 if rest is included) only has 459 rows in the Records part when viewed using fitfileviewer. So that is not even a per second record for the 9:41 that it says that I skied as an overall workout duration. If every second of the 1min intense intervals were recorded then there should have been 600 records presumably? The intervals that I created are 557 seconds in total so some of those seconds are ignored/compressed presumably in the FIT.
Hopefully you can download the FIT file from my record (via the Data tab in Timeline view) as I cannot load it here & then view it in a FIT file viewer & you will see what I mean. Or you can perhaps tell me what I am misunderstanding if that is the case. Without that I am not convinced that Intervals parsing or calculating method is the problem.
Dave