I often have a problem with Mac and Kobo Aura One (I haven't used my Kobo HD in a while). If often happens that when I connect Kobo (two original Kobo cables, Kindle cable, other cables) to whichever port on Mac it doesn't show up neither on Mac or in Calibre. Or sometimes it shows with third or fourth cable (always different cable, no rule). If it doesn't show at all, it usually helps to restart Mac and then it shows up. I have no idea what it is, but it never happens with Kindles I have. So I am guessing it's either lack of love between Mac and Kobo or it's Kobo USB port.
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