Duplicate Mods

A common but potentially game-breaking modding issue: duplicate mods in your RimWorld mods folder. While each mod lives in its own subfolder, the game ignores folder names. A mod's true identity is its packageID, defined in the About.xml-file file. Mods with the same packageID (e.g., different versions, forks, old/continued releases) are treated as identical. On startup, the game reads your ModsConfig.xml - a list of enabled packageIDs - and loads the first matching folder it finds, even if it's the "wrong" version you didn't enable.

Always unsubscribe old/unused versions - no exceptions. The game might silently load the incorrect version of a mod, with no clear warning. Sometimes you can spot it via errors that only make sense for the wrong version of said mod, but more often it can go completely unnoticed. Also keep in mind that the game always logs such duplicates - even if the mods are currently not on the active modlist and only sit there as inactive.

Keep your setup clean!

One additional problem with duplicate mods is widely unknown by people as well. If you're using two mods with the same packageID - one from the Workshop and the other one in your local Mods-folder - the game itself appends the packageID of the Steam version to differentiate between them (mod.package.id_steam.) Since mods use the packageID to optionally load content for cross-compatibility, that also means that a mod looking for a certain other mod by (mod.package.id) wouldn't see that mod if it has been modified that way. Thus the compatibility-patches wouldn't be loaded at all.

PSA: This potential issue has been mostly solved by changes made to the game in 1.6. Mods with those suffixed packageIDs now are treated as interchangeable by the game. This of course changes nothing about other issues from duplicate mods, but at least reduce one problematic aspect of it.