I've first noticed this problem about a week ago, ever since I changed the battery in my Fit Meter and after changing for Daylight Savings Time (not sure if either one of these are contributing to the problem, I'm just mentioning them as the only things I'm aware of that have changed), where the Wii Fit won't properly show the calories burned or progress on the walking/running challenge after syncing with the Fit Meter.
Note, also, that my parents have Fit Meters that they sync with the same Wii system--neither of them are having the problem I'm having, but to refer again to potential contributing factors, neither of them have had to replace their batteries just yet.
Here's exactly what happens: I walk about, either just the same day a few hours prior to syncing or for several days running (recall the Fit Meter is supposed to retain step count for about a month, so a few days is easily within the device's memory).
My activity level is the same now as it was more than a week ago, back when everything appeared to still sync properly.
According to the Fit Meter itself, I have walked those steps, burned those calories, etc. But when I sync it with the Wii Fit, it reports 0 total calories burned (e.g. nothing burned since the last time I synced it, whether that was an hour ago or three days ago), and no steps whatsoever on the walking challenge. Whether these are two separate problems or the walking challenge problem is a symptom of the calories problem or vice versa, I don't know; I just know both things are happening... or rather, not happening even though they should be.
What it does show, on the next "calorie" screen, is however many calories I might've burned since midnight (which is ironic since today's calories are part of the apparently nonexistant total, and especially ironic if the last sync was earlier the same day--in both cases, those calories get added to today's total without being added to the "since last sync" total), and it reports some progress, if any, in the altitude challenges, even if that progress is only 3 feet.
I took video of a recent session in which this happened, and I plan on taking another video sometime this evening after all my classes are done, to see if it's doing it again; I'll upload that to YouTube later and provide a link in here if need be.