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Randomly ejecting USB drives is a "feature" of Yosemite and El Capitan. It is being fixed again in Sierra apparently.

Yeah, randomly ejecting... but just ignoring devices completely is the thing that's making me mental lately. WTF is that??? Usually the ejecting is actually just pseudo-ejecting—it doesn't actually happen, it just says it does! (Which is it's own kind of mental...) But isn't plug-and-play a 20 year-old "technology"??? It's insane! Having to restart my rMBP, just to see my external drive, or audio interface. Hole s*** balls!
 
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