Persee does not reboot, no logs in sylog file

I need some advices.
I am using Persee with lubuntu16 img file.
My software reboots the sensor everyday at 12h00.
Regularly, the sensor does not reboot. It does not connect to the network. It does not answer to the ping. The only solution to get it started again is to unplug and re-plug the power supply.
Also, there is a blackhole in the file /var/log/syslog between the day of the failing reboot and the re-plug.
Has anyone encounters such problem?

Thank you very much for your help
Best regards