Irregular waking up from deepsleep

[hunmik]

The device is set to wake up every 600 seconds. At every second or third wakeup, it wakes up earlier by one minute, then it goes to sleep, and wake ups again 1 minute later at the right time.

Se below data received at MQTT broker, the wakeups in question are marked bold.
What is the reason of this behavior?

2025.03.27. 8:40:04(-9.24 minutes) {"DeepSleep":{"Time":"2025-03-27T08:50:00","DeepSleep":1743064804,"Wakeup":1743065400}}
2025.03.27. 8:39:07(-57.67 seconds) {"DeepSleep":{"Time":"2025-03-27T08:40:00","DeepSleep":1743064746,"Wakeup":1743064800}}
2025.03.27. 8:30:27(-8.65 minutes) {"DeepSleep":{"Time":"2025-03-27T08:40:00","DeepSleep":1743064227,"Wakeup":1743064800}}
2025.03.27. 8:20:06(-10.35 minutes) {"DeepSleep":{"Time":"2025-03-27T08:30:00","DeepSleep":1743063606,"Wakeup":1743064200}}
2025.03.27. 8:19:18(-48.49 seconds) {"DeepSleep":{"Time":"2025-03-27T08:20:00","DeepSleep":1743063557,"Wakeup":1743063600}}
2025.03.27. 8:10:05(-9.22 minutes) {"DeepSleep":{"Time":"2025-03-27T08:20:00","DeepSleep":1743063004,"Wakeup":1743063600}}
2025.03.27. 8:09:04(-60.46 seconds) {"DeepSleep":{"Time":"2025-03-27T08:10:00","DeepSleep":1743062944,"Wakeup":1743063000}}
2025.03.27. 8:00:31(-8.55 minutes) {"DeepSleep":{"Time":"2025-03-27T08:10:00","DeepSleep":1743062431,"Wakeup":1743063000}}