Wano, or more specifically many things regarding its plot, is a good candidate:
1) Gifters are firstly introduced as abnormal zoan users that, in spite of that, can transform without problem. Sheepshead is a good example of this since he can invoke his sheep parts at will, but fodder soldiers (like the wolf user in Zou) could do it too. Later it was retconned to a permanent change and gifters can't control their transformation anymore.
2) Kin'emon was firtst introduced as a retainer of the Kogetsu family and introduced himself in a very cold, formal way like if nobody there knew him. Raizou was then addressed as "dono" by Neko and Inu, and they explained how the relationship between the clan and the minks was very old. Only next chapter we get the feeling that Neko and Inu were close friends to Kin'emon and literal retainers of Oden, and the family is named as Kozuki, clearly seeming like Oda made some changes between chapters.
3) Again in Zou it was stated that the Beast Pirates were after Oden because of his knowledge on Laugh Tale, which was never addressed during the flashback.
4) Enma's background was retconned from a sword that was only tamed by Oden, nobody before, nobody after, into a birth gift (so it is impossible for a "before" to happen).
5) Orochi forgets that he knows that Hiyori is alive.
6) The Big Mom Pirates don't try to climb the waterfall after they're taken down by King and they somehow don't know about the secret port, which is supposedly used by different people affiliated with the Beast Pirates, in spite of being the crew with the best intelligence network in the world.
7) Marco's letter makes no sense.
8) Oden is allowed to keep his swords even imprisoned.
Am I forgetting something?