Uh, we have quite a mix up of different issues hiere in this thread. So where do we start?
1) Files not restored in version 2: The version 2 backup only contains the database content (playlists, lyrics) and not the audio files. You need to restore them seperately. If Dropbox does not work, you can use iTunes filesharing. But there is no general Dropbox issue in version 2. I just tried to download a song from Dropbox and it worked fine.
2) If you try to load a bunch of songs from iCloud or Dropbox into version 3, it is possible that the downloads fail. To work around this use the Files app to download the songs and once they are locally available, import them into Stage Traxx. See here how to import from the cloud: https://stagetraxx.com/user-guide/songs/#import-files
3) Restoring a file is simple. Just look in the song details in Stage Traxx which filename the audio file has and make sure that a file with this name is located in the Stage Traxx folder.
Have I forgotten some of the questions?