Board Thread:Theories and Speculation/@comment-36512555-20200101053037/@comment-32685487-20200416011230

Anime elaborated on it, https://www.youtube.com/watch?v=6Nofs_PanuY all the up to the point that it whited out and then right after showing that even as Kirin was coming down Itachi didn't have Susanoo active, no orange or red chakra around him nothing at 9:29. So yes Itachi did react to it.