My external drive will not properly eject in macOS.
An external drive (U32 Shadow, Shadow Mini, MiniPro, or other) will sometimes refuse to properly eject in macOS.
This can be caused by the Spotlight function in macOS. You can prevent Spotlight from searching the external drive, which may resolve this issue.
Go to System Preferences > Spotlight > Privacy and then click the (+) icon. You can then select the external drive and it will no longer be accessed by the Spotlight function.