The collusion quotes in this article start in October 2022, though it doesn't say exactly when the collusion started.
As far as I can tell, avian flu did create a supply shock, which did raise prices. When the avian flu problem started going away, the egg companies started colluding to try to keep the egg prices high.
> Meanwhile, in context and during the class period, egg producers like Cal-Maine increased egg prices by as much as 270% in 2023 despite having zero Avian Flu outbreaks in their egg laying hen layers on Cal-Maine affiliated farms (https://www.classaction.org/news/antitrust-lawsuit-says-prod...)
The criminal conspiracy part here was manipulating the index prices in tandem so that everybody raised prices in lockstep.
How much did supply go down considering that Cal-Maine Foods, Inc is (or at least was) the single largest supplier of eggs in the country? Ultimately their profits increased 718% (https://www.cnn.com/2023/03/29/business/egg-profits-cal-main...) which seems unlikely to be explained away by reduced supply. They were price gouging and fixing prices with the other large suppliers to prevent consumers from just switching to those brands while small egg producers may have had issues with avian flu keeping their fairly priced products off the shelves.
> small egg producers may have had issues with avian flu keeping their fairly priced products off the shelves.
They didn't had the product though! This is main part of the reason price went up in 2022. It's either that or no eggs on the shelves.
[0]https://agdatanews.substack.com/p/americans-really-like-eggs