Noel,
That looks pretty horrible and can only suggest that, since Kent didn't pick this up from the same files that I emailed yesterday, it may be caused by Dropbox.

re New file; I made several new files using these RTs with the BLANK34.STY and others, all with the same dropouts.

re XML; I have never used this.

Have just opened this song in RB using the right click menu, something definitely strange.

I have RB set not to generate tracks when opening .SGU or .MGU but this generated RT's and MIDI, complete with dropouts in RT2055 and its MIDI.
Also, instead of naming the tracks as normal, they are named BB RealBass 0: J_SWING, BB RealPiano 0 etc.

On a new track I generated another instance of RT2055, guess what, no drop outs.

Closed all this by selecting New file and not saving then re-opened from File, recently used. Generated as before except this time tracks are named
BB RealBass 2055: Guitar Acou, BB RealPiano 2055: etc. and only two MIDI tracks were generated.

Files made using BLANK34.STY and RT2053, 2054, 2055 behaved as above when opened in RB.

Tried a few recent .SGU or .MGU files that do not contain RTs 2053, 2054, or 2055; opened as expected with no tracks generated.

Tried your suggestion of opening in RB and saving as Newname.SGU, same dropouts when opened in BIAB.

In a new BIAB file re-entered the same chord progression using BLANK34.STY, then generated the same RTs as _CACTUS.STY substituted RT2055 with RT823.
The resulting .SGU has no issues in BIAB or RB.

This points me towards RT2053, 2054, 2055 as the problem.

I have a couple of work around that will let me move on with this song, but I really would like this to be resolved.