Looking at the packages, I find they not only use the same item ID (Prototype ID in Sims 4 Studio) but some of the CASPs and textures and all the meshes have the same identifiers.
CASP resources define each swatch. The item ID in the CASP identifies one item that shows up in CAS so all CASPs with the same ID are grouped together as swatches. This is why the culprit and victim are appearing as swatches under the same item.
The CASPs, textures, and meshes, like every resource used by the game, have unique identifiers in the form of a TGI - the Type of resource, a Group number, and an individual Instance number. The game can only load one resource with a given TGI - duplicates will replace anything previously loaded. In this case since there are four pairs of two CASPs, one in each package, with the same TGI, only one of each pair will show up. Similarly, with several pairs of meshes and textures, one in each package, with the same TGIs, only one mesh or texture of the pair will show up. You wind up with a mess with the wrong mesh and/or texture being used for some or all swatches.
Clearly what happened is that one of these creators copied the other one's package and modified it by replacing meshes and textures and adding or removing swatches, and didn't realize by not changing the identifiers it would create a conflict.
I don't know of any way to fix it in Sims 4 Studio without going into the Warehouse and manually changing identifiers for the affected resources and making sure all the links from the CASP are still correct. You can do it in CAS Tools by using the option to select a Custom Content package and clone it as new Custom Content - it won't copy the thumbnails but it'll give you a new package with everything else renumbered.
