Hey I just want to confirm this bug happens to me too, and I found a workaround, assuming you want to prioritize mynetdiary for calorie counting.
If you go to Samsung Health app settings, then Apps in the "Connected apps and services" group, press "MyNetDiary".
Enable write and read for everything, but uncheck "Nutrition" for "Allowed to read". This will force nutrition data to be one-way only: MyNetDiary -> Samsung Health App.
What's happening is some bug somewhere is forming a loop of reads and writes. MyNetDiary writes calories to Samsung Health, then reads to update/sync it's own nutrition data from the Health app, sees its own additions, rewrites those to itself as new data, then realizes it needs to sync this new data to the Health app, writes that to the Health app (duplication), etc etc and duplicates records many many times.
I knew something was wrong when Samsung Health was telling me I had eaten 30 taco bell bean burritos today despite mynetdiary only showing 1.
That syncing logic needs to be rewritten, just not sure which app is at fault lol. Really they could both prevent this from either side, so I'd blame both for not checking for this edge case (I'm a software engineer which is why I'm aggravated, but I don't work for either company).
Hope this helps a bit. Once you update those settings, it'll resync correctly and duplicate entries should disappear.
