Mods like Map Reroll (for starting tile) or World Edit 2.0 allow you to change terrain mid-game. If you delete a faction base or a blocked tile using these tools, the game sometimes retains a "ghost" reference. When the map tries to generate a caravan event on that deleted tile, it says, "Err site label detected new" because the tile is technically new, but the biome/faction data is gone.
Feature Name: SiteLabelValidator
Source: RimWorld.WorldGen.SiteDef
Error Message Pattern: "ERR: site label detected new - [VariableText]" rimworld err site label detected new
To resolve this error and improve robustness, implement the following feature upgrade: Mods like Map Reroll (for starting tile) or World Edit 2