Great job helping your little chick get better! Glad you're enjoying you chickens!
There could be lots of reasons those few aren't going in... but let's see, ten chickens need a lot of roost space to be comfortable. And if you said they're not quite a year old yet (though birthday in feb 2017 would make them almost 2) they could just be getting bigger and don't fit as well as they used to. Pecking order is a big deal, and if the other hens want more space, those on the bottom will get booted out. They all will need a
minimum of 10 linear feet of roost space (12" per chicken)... could be two 5 ft bars or three 3 ft bars, something to equal 10 feet or more, and be at least 12 inches apart and 12" from the wall. Remember, that's minimum. They actually need a bit more to have room to flap their wings and get up there:
How Much Room Do Chickens Need
Good luck with your flock!