I have the exact same issue, can’t play any audio using any application (other than Roon) using the same audio device after closing Roon.
If I switch to another audio device, like my USB connected gaming headphones, I can hear sound there.
If I switch back again, no audio.
I’m using a Meridian Explorer 2 as audio device, using the ASIO driver for Roon.
I have to restart the my Windows 10 Pro PC to recover.