Gpx sync between EXPORER 4 and GPSMAP 66 ST fails.

Gpx sync from new Explorer version 4 to GPSMAP 66 st fails. With the new Explorer version 4, a gpx track sync from Explorer to device fails, the waypoints are synced however. General Sync status is ok, so the connection between Ipad mini 5 and GPSMAP 66 st over Bluetooth is working. Only when an imported track into Explorer is synced to the 66 st, the sync status in Explorer will show fail (in red). Is this a bug in Explorer or do I need to do something??