My Vivoactive 4 keeps powering off after I save an activity and for longer activities it powers off mid-activity and won’t turn back on until I plug it in. When it does power on it shows battery at 50% ish so not due to battery running flat.
I have the same problem, please contact via email, I am in Mexico, yes you can access my account. My Vivoactive4 shuts down after saving a running activity. Garmin-Inder