I am getting the same problem. New out of box today (May 6, 2019). Just replicated the losing connection stimulus theory by putting my phone at one corner of the apartment and walking to the other corner. After waiting in the other corner for a little bit the vibration happened with no visible notification on the watch. Don't seem to get the vibration when I'm sitting with my phone for a long periods, nor do I remember it ever happening. Keen for Samsung to resolve this bug for a brand new watch.
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