Seems totally healthy and happy, but stopped laying

That does happen in the autumn, as our daylight hours begin to shorten. See, chickens really need a good 14 hours of daylight to lay eggs. Here in Ohio, it's getting dark very early now--around 6:30, so I have lights in my coop. I turn them on around 7am, and I turn them off around 8:30 or 9:00 pm.

 

First year pullets often will lay right on through the first winter if they start laying in the fall. Also, whether or not they'll lay in the winter depends on breed and where you are. I mean, some places just get more daylight than others. And some breeds dont' seem greatly affected by the lessening of sunlight in winter.

All that said, only one of my older buff orpingtons was laying this fall and now that ones gone broody. One wasn't laying, molted, then started, then stopped. One layed all summer like clockwork, and now she's molting. Then the broody. Good thing I have others laying or I'd have to buy eggs. The ones that are laying are first year pullet orps and I'm not giving them any additional light.