I'd been having the same problem with Samsung health not always syncing my step count to My Fitness Pal and after reading all the comments and trying a few people's suggestions it was still not working. I then started having a play around in the S Health app and done the follow which worked!... Not sure if it was a coincidence or actually worked!? Will see again tomorrow.
Scroll to bottom of S health home screen > click 'Manage items' > scroll down to 'feature apps' at bottom of page > click find more apps > it should then show My Fitness Pal (mine says 'open ' in green) > I clicked on it and it opened up MFP and updated the steps!...
Goodluck fingers crossed it might help some of you! 🤞☺️
I tried the "solution" at the first of this thread and it's still not changing the steps from 0 to the accurate step count shown in Samsung Health and on my Active 2. Cam someone PLEASE fix this issue? Samsung Health is horrible for food entry and My Fitness is useless unless it tracks my steps.