I had a similar problem with my edge 500 many years ago after Apple came out with a new version of OSx for my macbook. It wasn't Garmin that was the issue. It's just that OSx wanted to assume wrong things about what it was connected too.

After changing the defaults for how it saw certain types of usb connections, it again worked fine with my Edge 500. It's been a long time ago, so I can't really tell you what the exact issue was.

Most of the issues I had when using a MacBook were Apple's attempts to "protect" themselves from what they considered infringement of others.