Passport 2TB randomly switches to Read Only on OSX

I have a 2TB Passport, formatted in Mac OS Extended (Case-sensitive, Journaled.)

It is attached directly to a MacBook Pro retina without a USB hub, and over the last few weeks randomly switches to read only until I eject. unplug and then plug it back in.

Any idea what would be causing this?


Have not seen this before.  Have you tried in another Mac? Do you receive the same results?