I would nix the ACV, it can interfere with calcium uptake.BTW, I am also using ACV, probiotics and just started electrolytes in their water as the temp is creeping up. Could that be it?
Nix the probiotics too, unnecessary....
...and just give a dose of EL once a week, always have plain fresh water available also.
What all and how exactly are you feeding?
Protein and calcium percentages of chicken feed given, please.