When I have sluggish or not very healthy-looking birds, I use poultry nutri-drench to give them a boost and get them up and going. I have used it a lot with very good results.
And just remember to just ask if there is any other problems or questions you have there is some very knowledgeable folks on here that are more than willing to help.
One thing to help with them being so skittish is to not come at them from above always try to move towards them from their level. Reaching from above triggers instincts of predators attacking from overhead.
With it being only the white birds sounds like it could be poor health of, or something passed on from parent. Nothing going on with your other varieties?
Don't see anything wrong with your other info just a little warm on the heat but that shouldn't be causing this. I start out about 95 for a few days then slowly drop a few degrees every few days.