I just ran into this nonsense today: it's raining, it's cold, and I want to have a warm seat. And I don't want the AC on. I found many threads like this one without a decent solution, so I figured I was probably out of luck... But then after about 20 minutes of fiddling with it (which is far longer than it ought to take to turn on seat warmers), I stumbled across this:
If you press the "..." icon in the center to open the app drawer, then long press on any icon to go into edit mode, the individual seat warmer buttons (as well as the front/rear defrost) appear and you can drag them back into the main bar where they should be! Hope this helps someone else avoid a headache.