Jim, was the Lock/Unlock option in settings already enabled by the case magnet before your Air 2 was updated to iOS 8.1.3?
Maybe those iPads updated to iOS 8.1.3 before the setting is enabled are the ones that lose the ability (or so it seems) to have the option triggered by the magnet.
If this is a new "feature", I sure don't understand it. 😕
To the OP:
Did you ever try to reset the device? Maybe that will knock some sense into it. It's always worth a try:
Device Reset (won't affect settings/data/music/apps/etc)
1. Press and hold (& continue to hold) BOTH the Sleep/Wake button & the Home button.
2. Continue to hold BOTH (ignoring any other messages that may show) until you see the Apple logo on the screen.
3. Release BOTH buttons when you see the Apple logo and allow the device to boot normally.