Not all of my ANT+ sticks are being detected, any ideas?
What's likely happening is another application is using your ANT+ stick. The most common app is Garmin Express, which by default runs in the background when you are not using it and uses up that stick.
If you have Garmin Express installed then go into its settings and uncheck the option to have it run in the background...
Apply those settings then shut down Garmin Express. You can then load up Studio and should be good.