WD My Passport & USB Loader GX
This may seem obvious to many, but if your USB loader occasionally struggles to find your drive, and only a reboot seems to help, chances are the drive’s firmware is telling it to sleep after a certain period of inactivity. In my case a white WD My Passport needed to have its sleep time changed from 30 minutes to none using a tool from Western Digital’s website.
If one has an enclosure without modifiable firmware, perhaps disabling InternetConnect24 would be another solution.