When you have the ‘Export’ tab you need to select all the items you want to export. This means you have to select the tracks under ‘Multitrack songs’ and also the ones under ‘Playlists’. If you select a playlist to be exported uTool automatically selects all the multitrack songs on it as well.
Did you do this?
I do this all the time and it should be really simple.
Creating a new song, add it to a playlist (new or existing one) en select them at the ‘Export’ tab and it updates the USB drive.