I've had my 945LTE since launch and usage generally unchanged throughout.
Today, out of nowhere, I've looked down and the watch has been off - twice so far. I hold power to turn it back on and it starts back up.
Battery is at 55% and firmware is latest (17.30).
I will continue to monitor, but it's unclear what's causing it to shutdown all of a sudden - no new updates, settings changes or usage changes I can recall.
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It happened a 3rd time... all in the last 3 hours or so - and none that I recall in the previous years owning the watch. Weird?
And a 4th and 5th time still today (over... 6 hrs?)