MOTO G5 splus phone switches off automatically as whatsapp notifiction arrives

MOTO G5 s plus phone switches off automatically as Whatsapp notifications arrive when the phone on battery less than 50%. Its happening multiple times in the day as soon as the message arrives. The phone restarts and the message which was arriving gets deleted on its own and I don't see it once the phone switches on.

Tricks I have tried -did a phone calibration multiple times but doesn't help.