Hello, I have exactly the same problem.
I am using my UR22C together with my Windows Laptop and FL.
Now I bought an iMac Mini 2018 and want to use it together with FL and Logic Pro X.
At first, It worked fine, I could play back e.g. on youtube.
Also my Soundcard was detected by FL Studio on Mac.
When I then downloaded Logic X Pro, and tried afterwards to restart FL (after heaving restarted the system).
The sound card gets ‘lost’. I will have to remove it from the USB, then plug it in again.
It is recognised again, however, only if I do not open one of my 2 DAWs (see above). Then, the connection will be lost again.
I already have the newest Catalina and installed the drivers.
What can I do?
It doesn’t work on USB 2.0 mode either.