The Garmin pilot aid needs to download the current FAA maps with all the restrictions, so instead of just going to fly, the pilot now needs to read and chart all the advisories on his path. With the loss of pilot skills, that may turn many small planes into paper weights until that is over.
For the fitness apps, they use the app to download information from the limited memory on the smart watch to the Garmin servers so the data is available to all the user's devices, and now that's gone. Then, either the user has to manually delete data to make room for new data and potentially lose the records, or find a cable for a direct connection.
The failure is that many users no longer have full access to a device because computers at Garmin got hacked.