Looking at your tracks in Schumn3b, I suspect the trouble is in "Track 8, Strings."
First of all, it's a Multi track (switching from one instrument to another in the middle of the track), which is something I believe UA dislikes.
But the bigger problem I see is that the track has 794 events. I notice problems with my .XMIs if there are more than 500 events in a track.
I also notice problems if too many events are set to start at the same time, but I've not calculated what the tipping point is on that. If I find my .XMI is stopping prematurely at a certain point in the tune, however, I check to see if there isn't a log jam of events trying to all fire at that point.
On to another question: well, there are instruments that will play softer than normal in UA, and plenty that sound different than in most midi players when heard in UA. The Instr.ad file can make a difference, and there are differences in what a SoundBlaster configured UA makes your midi sound like as compared to a Roland. I go through a lot of trial and error to get my tracks to sound reasonably nice for a SoundBlaster configuration, trusting that they'll sound, if anything, better for Roland (which is normally the case).
Music varies more than any other aspect of UA from computer to computer. There are quite a number of factors involved. An author can only try to produce something that works well for their machine and hope that it won't sound too badly for their players.