How often it happens
This bug occurred at the start of the Survival reset. The Eater of Worlds was dead before we fought any bosses. There was never a message showing it had been defeated nor spawned.
Oh perhaps the boss did get defeated but before the new cycle started, so the meteor fell when the world was fresh from the reset, this issue can happen too with npcs arriving despite their conditions not being fulfilled (but in the moment before the world reseted they did) an example is the Pirate npc arriving in pre hardmode and giving people access to the cannon