vivoactive 6 sometimes vibrates and the only way stop it is to restart other times it just shuts down with no warning. staff at london marathon expo tried to fix but its still doing it. Any tips?

Watch vibrates and won't stop - then have to restart 

or it receives a notification, vibrates and then can not clear - then have to restart

or it just shuts down with no warning 

could not rely on it for marathon so had to use older garmin