I had a similar problem with two identical My Passport for Mac 2 TB drives I purchased in January. When the Mac woke from sleep, no files or directories were visible on the drive until I force-ejected and remounted them. I went back and forth with WD tech support for months. I tried everything they suggested, and nothing worked. They replaced one of the drives with a My Passport Ultra, and it failed even more catastrophically-- when the Mac woke from sleep, the drive’s partition table became invisible to the O/S, and I had to reboot in order to get it back. WD tech support was quite difficult to work with, since the case would often be assigned to a new tech support representative every time I replied, and even when it wasn’t, they kept responding as if no one had read the conversation thus far. I had to keep repeating myself and answering the same questions over and over again. I finally stumbled upon this thread and was inspired to try uninstalling all WD software (including WD Utilities) from my Mac. It appears that that solved the problem. That’s a shame, because I also use a My Book Thunderbolt Velociraptor Duo, and WD Utilities is the only way to check the RAID status on the Duo.