What data does the Garmin output? GC might not be recognizing something in the data file, or it might be interpreting the data file wrong. It might also be that Garmin recently changed the way it outputs data. That's an eternal problem with "do everything" software. If something changes and the developers aren't keen to the change, then it will all of the sudden lose compatibility. On second thought, definitely something to bring to the developer's attention.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter