As the vivoactive doesn't have a baro sensor for elevation, and it uses GPS, which is usually very inaccurate.
when importing activities, "elevation correction" defaults to disabled, so you get really bad elevation info. If you manually enable it (on one activity at a time) it's much closer to reality.
This is like the fr15, but there, elevation correction was "enabled" by default on all activities.
This is a GC issue and not a vivoactive - that's why I'm posting here.