Found a possible fix!!
Finally figured out how to get this working after much frustration; I think someone else may have posted they got it working, but gave no detailed instructions. I have it working on a 1st gen iPad mini, iPhone 3gs, iPhone 5 and iPhone 6.
I take no liability for this fix, the app not working, or any related issues. DO AT YOUR OWN RISK.
1. Start fresh. Delete the Garmin N.A. app from your phone/device.
2. Install the Garmin N.A. app from the App Store.
3. Open app
4. Follow on screen menus to the dialog that allows you to download map sets
5. There are two items you’ll need to download.
First, there is a set of “core” files that must be downloaded.
Second, there is the map data set you purchased, in this case the North America map set.
Tap on the download button to download each of these. Find a place with fast internet or be patient.
6. Wait for the downloads to complete and do not close the app. If you are prompted by the first core files download to restart the app press “ok” and continue waiting for the North America maps to finish downloading.
7. (IMPORTANT STEP) AS SOON AS the North America map set is finished downloading it will prompt you to perform an app restart. DO NOT RESTART THE APP! At this point press “ok”. Then Hold the power button on your phone until the shutdown slider appears.
8. Wait for the phone to shutdown.
9. Hold the power button until the Apple logo appears on the screen. Wait for the phone to reboot.
10. Open the Garmin North America app and you’ll notice that the app can now access the map data unlike before and can calculate a route. Voila!
Dear Garmin,
I feel like I’ve definitely cut you some slack here by giving a 4. I hold Garmin in high regard in terms of navigation and would trust my life on it. Overall it’s a great app, a 4, but if it’s unreliable, it’s worth a -5. I purchased this app so that in a pinch, without cell service, I wouldn’t be stranded. If it doesn’t work when I expect it to work, I’m stranded. For the sake of the company, please consider a) making a prominent post to your website to explain a temporary fix or b) release an update that remediates the issue altogether. Garmin, you are one of the biggest names in navigation and if I ever own a plane I will buy Garmin for navigation. For integrity’s sake fix the app.