I just pulled unstable, built it and tested View Scene Here' opens my route OK.
However, you may need more than 5 seconds or another method for densely populated tiles that are stored on slower I/O media.
I closed the ContribTrackViewer process, restarted it, selected the route but when I attempted to open the viewer at the same location in the route, I also got the blue sky and black ground. As I could replicate this issue, I tested with Process Monitor and Process Explorer. I observed that when the viewer was open, the reading of the route files slowed down considerably.
A work around is once the viewer is open, wait ~10 seconds for a number of the route/global files to be read, then close the viewer. When the viewer is closed the reading of the route/global files continues but at 'normal' read speeds. Wait 10 seconds then open the viewer again at the same location and wait 10 seconds. Keep opening and closing the viewer with 10 second intervals between at the same location on the route and the viewer would finally open and display correctly after all the route and global files had been read into memory. Highly populated tiles took 3 attempts and lower populated tiles took 2 attempts to open successfully on my computer.
Once the viewer is displaying the route, this part of the route remains in memory so subsequent opening of the viewer in the same location is instant. If you go to another location in the route you have to go through the same process of closing and reopening the viewer to allow all the route/global files to load before displaying correctly.
Hope this helps.