Mass Storage on the Enduro2 is not functional (Version 9.36). The Device defaults to MTP Mode, regardless of the system setting "Garmin / MTP (Media Transfer)".
That has a lot of implications, e.g. I cannot use BaseCamp and it's neither possible to upload custom map images to the watches Storage. Garmin Express has no issues, however.
Is this a known bug in the current firmare or is my watch broken?