I’ve run into the same problem and the solution was the labels file. If you check the example label files in the ngc containers you’ll find that detection gies have newline-separated labels but classification gies have colon-separated labels. Switching to a single line, colon-separated label file fixed it for me.
This is one of the many issues arising from the severe lack of documentation and consistency across the several otherwise excellent tools that NVidia provides. Whenever I run into silly bugs that torment me for hours/days I call them “DeepStreams”.
Btw, the targeting to the tracker is a no-op. Without the tracker you should observe that it does not crash but it does not do what was intended either (at least my case was as such). The tracker actually exacerbates the issue.