Problem viewing Basecamp contents in Google Earth

I've noticed that when I highlight a folder of routes in Basecamp and click "view contents in Google Earth" that not all of my routes are shown.

Most are and are highlighted purple as you'd expect, but for some reason other routes just aren't there. It looks like they might be showing a thin white line.

The odd thing is, that if I just select that particular route in Basecamp and click to view contents in Google Earth, it shows up as a thick purple line, just like I was initially expecting to see.

Anyone else come across this?

What's the easy fix?