I noticed this no twice in a row, before and after the update to SW-Version 5.90. When I used the ski app during the day it would show me around 3000 burnt calories in the evening, of which around 2000 active. When then synchronising the data with the android app in the morning after, I would only see something around 2500 calories the day before and also on the watch itself the number changed.
Furthermore, I noticed that in general, if activities are synchronised the other tracked numbers are often not right on the first synch, like steps, active minutes, floors, calories. When then synching a second time after the activity was synched, the other numbers were then also correctly synchronised.