Garmin Express is causing your device to be kicked out of Garmin Mode and sending it back to MTP Mode. If you do not wish this to happen, close Garmin Express so that it is not running in the background of your computer and your device will stay in Garmin Mode.
So it's been almost a year and the bug is still there...
When can we expect this to be fixed?
well yes, this seems to be the case. But the sole reason why I am connecting my phone to the computer is because I wanted to use Garmin Connect to update the firmware of the device.. but I can.. so, chiken/egg situation.
I meant "but I can't"