They may well need more protein.
Layer feed is minimal in protein(~16%), the cracked corn is diluting that protein - maybe significantly depending on how much in relation to layer feed.
Either free feed a higher protein feed or stop with the cracked corn.
Oyster shell should be free fed in a separate container.
What wormer did you use and when....all birds or just the olders?
Did you enact a withdrawal period?
X2 i was asking about the size because from what I have noticed in my own birds is that the more production geared birds(sleeker) require less protein than the stockier built ones like dual purpose birds so I would either (have less corn, or add feather fixer, soybean meal, meat bird feed something that has a higher protein value than the layer feed that can help them get back to laying )