For me, Garmin Connect no longer syncs with MFP (MyFitnessPal.com) since 29 Nov 2014.
I tried, in MFP, disconnecting Garmin Connect, then reconnecting--but, no joy! Tried that a couple of times--once when I was already logged into Connect and once when I was not. The first time took me straight into Connect Dashboard; the second opened Connect, but I had to log in.
I looked in Connect-Settings-Account Information. Under the heading, Applications, only Training Peaks is listed (previously, both MyFitnessPal.com and TrainingPeaks.com were listed). Connect only allows me to REMOVE applications in the Settings menu, but not to ADD applications. Connect should have an intuitive method of adding applications to that list and to allow them to be added with permission to READ only or to READ & WRITE/MODIFY.
Why hasn't Garmin even bothered to post to this thread in nearly a month? A simple note from Garmin posted, periodically, to indicate that they acknowledge they are working on a solution (or, have discovered the problem is with MFP) would be progress. Seems to me that Garmin is close to a "Customer NO SERVICE" policy!
I also have the problem where Garmin Connect (website and Garmin Connect Mobile IOS app)is not being updated by MyFitnessPal for calories consumed. If I force a synch via Garmin Connect website it will update. Forcing synch via Garmin Express mobile also does not work. This has been going on for 1 week now