Regarding Dropbox, there is nothing I can do as there is no Dropbox specific code in Stage Traxx. The Files integration of Dropbox is really buggy and only Dropbox can fix that.
Regarding your other problem: could you describe what you mean by "blending"? Stage Traxx is files based. Make sure you have unique files names when adding tracks. If your files are always named something like "track1" then they will overwrite each other. This is not specific to Stage Traxx. It is how file systems work. So make sure you name your tracks something like "songname - track1".