Hi,
I have random elevation spikes. Very high, like -6000m or +9000m.
That isn't a device problem as GPX export to RunKeeper or Endomodo shows correct elevation values.
That's started only yesterday.
Here my 2 workouts. Both were in clear areas without obstacles (seaside and mountain run), no buildings, no trees, clear sky.
http://connect.garmin.com/activity/485244800
http://connect.garmin.com/activity/485857696