Yes, I read years ago that chickens shouldn't be fed more than 27% Protein feed as it can lead to kidney disease and gout.Possibly another poster? @GC-Raptor mentioned reading something about 27% being the limit for chickens in something they read right before I responded in that thread. May be what you were thinking of?
Over 21% Protein can cause watery poop and high ammonia levels in bedding.
This is for confined Adult chickens not offered Scratch Grains or access to vegetation to lower daily Protein intake.
Recommended upper level for layer chicks is 22% Protein so as to not induce a too rapid growth and early onset of lay. GC