I am seeing this more and more. The PDF is generated before the report completes.
Orion Core 2012.1.1, NCM 7.1, NPM 10.3.1, NTA 3.10.0, IVIM 1.3.0
The issue has been fixed in one of newer NPMs, I guess 10.5 from the top of my head. NPM 10.5 it is. In case it still won't work with default, there has been added extra settings to increase export timeout in conf. file.