What is the output of these commands:
ls -l /Library/Extensions/*USB*
ls -l /System/Library/Extensions/*USB*
macOS High Sierra isn’t exactly the latest version. I’m not sure the Apple driver for CP2102 was already included in that version. “Resource busy” usually indicates that two drivers (from Apple and SiLabs) are fighting for the same driver. But it might also be that the device is still open from another application like a serial monitor. Check that it is not the case.