Active calories drop suddenly in Apple Health despite staying active

So I am wearing an Apple Watch 7 all day and performing lots of trainings (walking, gym, cycling).

I have noticed now a number of times that the “calories burned” suddenly drops during the evening. A fresh example from today: Apple Health at 7 pm said I had burned 1111 active calories and 1700 in total. Here 3 hours later active calories are down to 1050 which is very peculiar because you burn calories just by walking around in your house/flat.

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Original Title: calories burned in apple health drops suddenly