Thanks for the explanations regarding logging.
I was in the process of enabling the logging and documenting each steps I was doing and observations, when I noticed something odd that I never noticed before: On the MC window header, where it displays the song title and progress, I could see that whenever I left the song on pause for a few seconds, it would change to "IPC" and the time progress would restart from 0, even though nothing was playing. Also whenever I would pause the song and restart it, even if I restarted it right away, it would always restart from zero. So it would not necessarily go back to the first song, but it would restart from 0 on the current song.
I started reading on IPC and eventually linked that to the WDM, which I use because my sound card is an external Audioengine DAC and headphone amp running through USB and using WASAPI.
So everything started fitting together: The reseting of song playback (pause restarting from 0, reseting to the first song, etc) is due to any other event on my laptop that steals the current process from the current song to another data stream, like a Windows sound reminder or whatever.
The solution was to create a zone and automatic switching. The recipe is clearly described in this JRiver help page:
https://wiki.jriver.com/index.php/WDM_Driver"Problems With Streaming Video Using Media Center's Internal Browser and/or Erasing Playing Now".
Once I did that I had no issues with Pause.
The only thing I need to figure out now is that I think I need to create a zone for online music player. I listen to Pandora through JRiver so that it can pipe it through my external DAC. But at the moment that does not work with these new settings.
As a general comment, I think this whole IPC thing creates a lot of confusion. Isn't there a way to have this pre-configured so that it can do the switching between zones by default?
Anyway, I'm really glad that now I have it working!
Thanks,
Ben