M31 has Exynos 9611 processor and it's a famous for it's auto restart issue since 2 years. Sadly though, It can't be fixed through an software update. Motherboard replacement is the only solution.
And now the auto restart issues is occurring in other devices too, those without Exynos 9611. I hope it's not a manufacturing defect as it seems to be since not every device is facing the issue.
I am facing the same restart problem with Galaxy M32. Samsung is giving updates nowadays to brick your phone, and when you call the customer care they will say your phone mother board is having some problems. While it's clear like day light that it was caused by an update given by Samsung
