This may have something to do with the Daylight Saving Time changeover this morning, as the sync time in MyFitnessPal is wrong (and, oddly, NOT off by exactly one hour), though that could also be only an MFP problem. It would also be a somewhat odd cause, as the changeover happens at 2 AM, so the start time for the daily count from which the cumulative total is measured should have been unaffected.
The cumulative calorie count displayed on my Vivosmart 4 tracker does not match the cumulative calorie count in Garmin Connect Mobile (Android) under the Health & Performance -> Calories view. My tracker lists 1,973 as of right now, while the app lists 1,888. I synchronized through the app, and I also tried synchronizing through the dongle and Garmin Express, with the same result. My tracker has the latest firmware available as of this posting - 4.90 - and the app version is 4.40, build code 5807.
I noticed it today because the negative calorie adjustment in MFP was substantially greater than seemed reasonable - it's usually consistent with correcting for the RMR calories included in activity calorie counts - so I checked GCM directly and noticed the difference, hence I suspect it's a new problem. The problem isn't that GCM isn't synchronizing or updating at all: the GCM cumulative count is updating with subsequent sync operations - I'm now at 1,982 on the tracker and 1,899 in the app, having synchronized again since I started this post.