How old were the chicks when you started having problems?Well The problem was found and I am posting so that any other new chicken person can avoid this. I learned the hard way that chicks need a gripping surface, not smooth paper or other smooth surface. My chicks were spraining their ankles and knees. Simple solution that nobody mentioned when I looked for help. Switched to pine shavings and no more trouble. I feel really stupid for my error so pass this on to any other new feathered friends. Nobody mentioned this key piece of knowledge that everybody else seemed to take for granted.
It is not recommended for day old chicks to be put on newspaper because of the slippery surface, and the possibility of the chicks developing spraddle leg. In your first post you said they were 2 weeks old. Chicks of that age should not develop that same problem as they are more muscled and coordinated.