it happened a few day after Marine HQ war, it's not something to do with Issho or Blackbeard..Issho first appearance is in Dressrosa, and Blackbeard still find his best after reforming a group and killed WB..
about the Alien? it's kinda funny but still arguable..what the hell just the alien do in the One Piece world?
Enel and Shiki? a think is not the time for they to comeback..
my opinion is, that's just an anomaly in the New World..just like what happened to On Air Pirates..
about the looks like of floating devices, i think it just the shape of the island or an anomaly in New World..