This Western Digital USB based external drive no longer mounts correctly on the customer's MacBook. The data is hardware encrypted from the factory. If this model WD hard drive fails on you, removing the HDD from the enclosure and connecting to computer will not allow for a successful recovery, because the data will be encrypted, therefore not mounting the data volumes correctly. In device management, it will likely show a RAW volume with the correct capacity.
How to recover the data? Will need a healthy compatible WD USB bridge, or advanced tools (advanced data recovery companies have them).
This WD model drive encrypts data on the fly based on factory design via the USB bridge. If the external drive becomes damaged and need to recover the data successfully, you will need a compatible USB bridge or help from an advanced data recovery company with advanced decryption tools.