Minecraft wiki entry for Custom_maps, associated text: A lot of maps don't require prior knowledge of the player playing it before it is loaded for the first time, and most of the time the final release has no reason to keep old player data generated by the developer(s). If your map doesn't require any playerdata, such as someone's advancements, position, inventory, or otherwise player-specific data, you can remove the "advancements", "playerdata", and "stats" folders found in the root of the map folder. If your map has custom advancements, do not delete those. Only delete the advancements folder inside the root of the map. (.minecraft/saves/Map_Name/advancements, not .minecraft/saves/Map_Name/datapacks/Maps_Datapack/data/namespace/advancements)