I noticed an interesting issue today (two, but one I think is an Apple issue) with the distance in Apple Health. It appears that Garmin is writing duplicate records. It looks like it's writing the total distance as a one time shot instead of incrementally like Apple does. Here is an example from a week ago (and this pretty much is the same almost every day) with some screenshots to show the issue. You can see my true value of distance for the should be 7.6 miles but Connect wrote two 7+ mile values (neither of which is right but close). The steps so far appear to be accurate.
I hadn't really paid any attention to this until today I got a notification that I met my move goal in Apple Fitness. That was weird because I don't have an Apple Watch. Apparently with iOS 16 (I installed the RC yesterday) it now supports movement from non-Apple watches. This leads me to the next interesting thing I found (which I think is actually an Apple bug but posting here just for visibility as I plan to submit a bug report with Apple). Apple is not recognizing the Connect values for distance and is using not only the Connect distance but also the distance the iPhone registered. I *think* it might be due to the fact that Connect is only writing a single value instead of writing multiple values during the day like the iPhone does (or like they do for steps which is accurate). Screenshot below of my distance for today including a 3.56 mile walk. The walk showed up correctly in Apple Fitness and matches Garmin. Garmin wrote a total value of distance for the day and Apple Health is showing a way larger value (which appears to be both the Garmin value and the iPhone values).