Same issue here for both my husband and me. He has a Fenix 3, I have a VivoSport. We have both been through about four cycles in the last couple of months, each lasting 5-6 days. During this time our activities are duplicated on My Fitness Pal 4-5-6-7 times. Even when we delete them, they come back. Even for prior days. It's not really possible to track anything if you have to constantly correct the activity calories. Sometimes even as I am deleting them, duplication occurs again! I have contacted MFP and they, predictably, say it is a Garmin issue. I suspect Garmin will say it is a MFP issue. Is there some way the two could come together an resolve this?? It would be great to get some feedback on this.
Has anybody figured out the problem yet or got a reply from Garmin? I found another thread where someone asked if the person has Strava & Garmin Connect linked to MFP... I had both linked and I’m sure the duplicate was due to info pulling through from Garmin Connect & Strava. I disconnected Strava now from MFP and will check tomorrow after my run to see if the problem’s been sorted out.
Look at my comments in this post linked below on using RunGap as an intermediary. It has helped me with many issues . (not specifically MyFitnessPal) but the same principles apply. Yes its an extra step but having control is great!