Apple Watch Ultra battery drains even in 'Low Power Mode' overnight

Hi!

Since watchOS26, my watch drains the battery during the night. I wear it all day with 'always on' display and battery is good. When I go to bed I take my watch off and since OS26 it automatically goes into 'low power mode'. After that the watch starts to drain the battery, and fast. See the battery drain graph.

Any ideas as to what's going on?

[Re-Titled by Moderator]

Original Title: Battery drain in 'Low power mode'