Roon switching Mac audio off?

I must be missing something. Roon Core runs on my IMac upstairs and feeds a Roon Ready amp downstairs. All sounds great. However when I use the Mac for other purposes with audio eg FB clips) I get no sound. Either through the Mac itself or outputting to a USB dac/ amp. I tried varios Settings in Roon and OS to no avail. To restore sound on the Mac I have to reboot. Is this right ?