I have a 620 and in recent weeks it has rebooted after about 4 minutes if I start to record a second activity. It has the latest software according to Garmin Express. There are other reboots that sometime occur shortly after I save an activity but I can't find a common point except that I have recorded on activity and sometime later it reboots. But if I stat a second activity then it seems to reboot again after 4 minute 30 seconds. Today there was over an hour between the first recorded activity and the start of the second. I have no sensors connected and the phone is out of range when it happens. Any ideas what is causing this?