This is happening to me too and other people so it look it's a bug with the latest updates adding mandatory 2-factor authentication to Samsung accounts. They'll have to to patch this. In answer to your above concern, no I think our data is stored in the cloud so it should be there when we get back into the app, I also think the Samsung Wear app is what syncs the data and the Health app just reads it so I'm going to keep syncing my watch in the meantime.
May I ask which device are you using so I can provide the proper help?
Have you attempted to wipe the system cache partition recently? Doing this is a good step to do after an update.
Thank you for confirming this.
I would recommend reaching out to Samsung Health, you can reach out to them directly at 1-855-795-0509.