@jctcom I know this post is now a bit old, but, I am thinking perhaps you have the same problem ongoing. I wanted to let you know of one tweak I did that has totally solved any and all issues I had related to JRiver and gapless playback, random hang-ups and non-play issues and so on.
What I did was cave in and buy another piece of gear, for $150, a WiiM Pro. I plugged this into my network and then ran an optical cord from it to my Yamaha A6A into one of the optical in jacks. I did this primarily as the WiiM Pro is a Roon endpoint (Roon Ready not just Roon tested) but I discovered that JRiver found it right away too as a streaming endpoint. So I have been testing it now for a week and it works flawlessly for me. No hang-ups, all gapless playback, sound quality is just as I expected it and of course with the optical out in use the device just acts as a bridge on the network to the A6A. For the price you might think about giving it a try. Also, since it talks to everything on the network it does not even rely on being visible so I can tuck it behind the A6A and have it out of sight and out of mind. I just switch to the appropriate input when I want to hear music from Roon or JRiver via my computer (or phone or tablet) and it plays away.