My Series 4 has been crashing/ rebooting repeatedly since update. Sometimes a self-reboot, more often a total blackout, and inability to reboot, or start of reboot and goes to black again, requiring putting it on charger, where it boots up and usually works properly— most of the time, not always. It does this regardless of whether charge is at 15% or 85%. I’ve not established any correlation with car audio, earphones or other peripherals, amount of charge, or WiFI. Right in the middle of a walk, no peripherals, iPhone 11 Pro in pocket, it may crash. Inconsistent and distressingly unreliable. Prior to update, it never crashed.