I recently upgraded to a Garmin Fenix 3 HR from my Forerunner 630. After a few runs with the Fenix 3, I realized that in Training Mode it does not do auto lap. I have a custom training workout for a 10k with no repeat modes in it. This workout was what I used on my FR630, and it used to auto lap at 1km. That no longer happens in the Fenix 3 HR.
Fenix 3 HR: 4.70
Forerunner 630: 7.50(bdd586f)
After googling around, I understood the auto lap under training mode is a feature only available to specific models/software versions. One of the reasoning behind it is auto lap might create issues if people are training in intervals larger than 1km. Breaking into laps at every 1km will make it harder/nearly impossible to compare their intervals. For workouts that you want auto lap at 1km (or at any custom distances), you can use Repeat feature as shown below. Setting up the workout as 10 x 1km helps to analyze the run at 1km intervals.
Depending on the model/software version of your Garmin watch you might have to tweak your workout plans. Hope this helps