I have the exact same problem and I couldn't figure it out. Nothing changed and not even a single setting on the watch has been changed. But all of a sudden it started to leave me alone in the middle of the day due to high battery consumption.
It shouldn't break the ip rating for moisture & dust if the battery is replaced by a Samsung Service Center - You can always inquire about it prior to having the battery changed - But the watch won't be much good if the battery is dead anyway 😉🐧
I bought the gear S3 Frontier 3 months ago and I have the same problem since the last up to date. I think that it's a Samsung problem. It's call: Obsolescence programmée. Many people have the same problem when you read on the net. Hope they Will find a solution . . . and fast