Yosemite and Garmin GPS - USB Problem?

Since installing Yosemite on both my Mac Mini and my Macbook Air I've been unable to establish a connection between, the app Garmin Express and my GPS, a Garmin Zumo 390 (motorbike navigator).

I've tried using different USB cables, different ports on each computer.

Sometimes the computer connected symbol appears on the GPS but only briefly, but the software on either machine fails to recognise it.

It may be a co-incidence but could there be an issue with Yosemite?

I've been discussing this with Garmin on its forum website. The folks there don't know what the problem could be.

How does one flag potential bugs in OSX to Apple?

I thought that perhaps it may be a hardware fault (either the USB cable or the navigator itself) but it works fine on my wife's WinPC.