Say that Company A is an online platform which hosts user-generated content, and to do so Company A requires in its ToS that users license said content publicly under Creative Commons License X.
Further than that, say that, at some point, Company A releases those contributions under a more permissive license, Creative Commons License Y, in a way that goes beyond the permissions granted by the copyright holder. (For the purposes of this question, assume that (i) the licenses are incompatible, and (ii) the ToS does not give permission to license the content under license Y.)
And, moreover, say that some third party, Website B, pulls that content and hosts it, with correct attributions, under License Y.
Where does that leave everybody in terms of license violations? Company A is definitely in breach of the license terms for its incorrect distribution of the works, but is Website B liable for its redistribution under License Y, given that they got it from Company A, making the fair assumption that their distribution under those terms was appropriate? Is Company A liable for the downstream redistributions of the works by other actors? What recourse do the copyright holders have to stop distribution of the works under License Y from those downstream actors?
Please keep answers general as regards to the licenses X and Y -- the change could be something as noxious as going from CC BY-NC-ND to CC BY, but also a smaller violation, such as a switch to a later (but incompatible) version of the same license.