I had a very similar problem with my 51mm AMOLED from yesterday to today, spent the whole time looking for the cause and felt I had tested everything possible. I probably found the solution in the German forum. In my case, the "Send heart rate" function was activated without having consciously switched it on. This could have happened during the last firmware update, because other settings were suddenly reset afterwards. Now I am confident that the battery consumption will return to normal after deactivating the function. Maybe it could also be the cause for you...
Fitness -> Heart rate at wrist -> Status = deactivate
