Using unified diff, looking at a new file. When I first click on the file, it only shows the first 3 lines. If I then scroll or click on the diff, it then renders the rest of the file.

See attached screen shots.

Stash v3.5.0 on Chrome version 38.0.2125.122 on a Mac (OS X 10.7.5).

I tried it with Safari version 6.1.6 and it works fine. Perhaps it's Chrome related.