I'm dealing with the same thing. I got the phone on October 3, and three days later it's randomly restarting. The phone either reboots 6 or 7 times before starting on, or refuses to turn on unless it's hard reset. It did have the 25/07/19 update when the problem started, but I have since reset the phone to factory default. The reset to factory default hasn't helped at all.
Model Name : ZS630KL
Firmware version : WW_16.1220.1909.193_0
Rooted or not : Not
Frequency : 12 times, and counting!
Please help! This is incredibly frustrating! Thank you!