I had the same problem, the phone rebooting 2-3 times a week.
The support was investigating the problem and they wrote me there was something bad in the way the connection with my operator was managed. We were looking to better understand the problem when my company changed their phone operator and with the new one the problem disappeared. At that point we had to stop the investigation and never found the real solution.
However, meanwhile I had found a workaround…
Do you have two SIMs installed? If so, change the configuration of the SIM you DON’T use for data connection and set “network type” to 3G. In my case the reboots stopped.
Ciao,
Max