Which version of Mac OS X that you have? When importing under the "Device" mode, Lightroom relies on the Mac OS X ImageCapture API to enumerate and provide the thumbnails from the device to display. It looks like the Mac OS X ImageCapture API does not understand Fuji X-T2 Compressed RAF file format. Try import with the "Files"/"Folders" mode as a workaround. Or try update your OS to the latest version of Mac OS X to see if the issue is fixed.