Daily crash or shutdown or energy save or else?

Home Assistant 2021.12.10 , Home Assistant OS 7.2
Running on rpi3-64
Everything works like a charm. HO, ESPHome, AdGuard, SSH. Very smooth. No errors.

But I experience a daily shutdown. Or crash. Or whatever. I need to re-power up my Raspi! It seems to stop working every 24h hours.

Nothing to see on the console. Nothing to see in /config/home-assistant.log or /config/home-assistant.log.1

I am able to login via SSH. But usual log files or debug method don’t work here, as dmesg shows the reboot, but not the crash. There are no useful logs in /var/log.

What can I do to to find out the cause for those daily stops?