I had similar issues with HDMI audio when I used that for years. Many friends of mine still do have the problem in Windows. It is frustrating.
I hate to sound like a broken record. I have recommended a Gefen HDMI Detective + many times here. But, it worked quite perfectly and satisfyingly for me for several years. Cost about $80.
Basically, it is inserted into the HDMI link, plug to plug with an input and an output HDMI cable. You set dip switches in the Gefen to match your system setup. The Gefen is powered by the HDMI link and is ON whenever HDMI is used from the PC. That gives it steady, unchanging HDMI audio/video properties which Windows always sees, even if your AVR/prepro is off. So, Windows never changes the HDMI settings via the handshake and JRiver never gets confused. The Gefen does its own handshake with the AVR, etc. as necessary, but Windows never sees that.
I now use USB for audio, but the Gefen is still in my system solving some display compatibility issues on HDMI video to my old Sony SXRD rear projector.