I have only noticed this since a recent Health app update (about 1 month ago?).
Since then my Watch 3 can barely make 24 hours without charge. I have checked via the Wearables app, and between 40 and 50% of the battery drain is caused by Samsung Health app on my S8+.
When I disable BT, battery life on the Watch returns to something like normal (approximately 48 - 60 hours to get to zero charge).
Leaving BT on, on the Watch, but turning off my S8+ altogether, gives a similar result, so it must be the Samsung Health app causing the problem.
Anybody got another solution to this problem?