I installed onvifdm last year and it works today on Windows 10 for me with IP2M-858 which has a substream2. But strangely it doesn't find substream2. Perhaps onvifdm would find your substream2. You could view and modify it there if desired and see what happens. Maybe something else in onvifdm could help...
I also just downloaded and installed onvifdm on another Windows 10 computer and it worked fine. Other programs I use that support ONVIF exploration are the android and Windows programs available at www.ipcent.com
Why did I write "Sounds like NVR problem"?
Because the post with Acti NVR says it works, and you said it works with web UI and VLC rtsp links. But after viewing your posts again, it's probably not an NVR problem.