Back again. I'm using my relatively new Windows 11 laptop now. FlexASIO worked fine with the Umik-2, but I realized that the same issue occurred, not recognized as USB mic. So I tried switching to Java in REW again. The Umik-2 is not even seen by the Java driver. The ASIO works without issue through FlexASIO, but I need the senstivity. When I started this thread I was using an old laptop from 2012 Windows 10. I had planned to dedicate it for that, but it's just too slow. The problem appears to be Windows 11 somehow. The Device manager sees it as Umik-2 with miniDSP as manufacturer, device type "Sound, video and game controllers". But in FlexASIO it's seen as Line (Umik-2).
(Later): I spent a lot of time trying to trace this down. The last thing I did was open the miniDSP UACS Control Panel. It has little control actually. It was set for 2 channel, 24 bits. I changed it to 32 bits not expecting any change. However, REW then found the Umik-2 in Java, accepted the calibration file and is now working with the senstivity set. Strange. The control doesn't even show the real serial number, just 000000. But it's working now.