I went out on my MTB on Sunday and tried out some of the new off-road data fields on my 830.
Grit and Flow both work as expected, and the 60s Flow field also seems to be fine - the pointer at the bottom indicates the current value, which matches the number shown in the field.
But 60s Grit is faulty. While the pointer at the bottom moved along its bar as I'd expect, the value for 60s Grit never once changed from 0.0 at any point along my ride, even as the Grit field itself incremented over time. (By the end of about 100 minutes of riding, the total Grit value was around 70.)
It looks to me as if the numerical value in the 60s Grit field is never updated.