Originally posted by Shaken_Widow:

not a bug, progression tracks to new worlds.

even though you didn't kill the elder on that world, the game recognizes that you were part of a world that had, and therefore have the ability to reach the next biome which makes those attacks happen.

this is why you don't bring a whelp to your friends server unless you're planning on making it your base server, only bring your chads over for parties.

Never was like you said
Raids are anchored to the world not to the character via killing bosses and some mobs
No matter if you have boss items from another worldseed , in another where the boss n mobs werent killed , raids will NOT trigger
This strat is used for builders seeds that want progression but not raids in their cities since EA release

For OP : only that i can figure is that you invited another guy in your world/server and he killed alone the elder and a troll to trigger troll and swamp raids