I believe this is a latent bug that has been around for the longest time and happens when you duplicate a blueprint. Inside the uasset metadata the asset is still linked on the viewport but the component metadata has been decoupled. I usually have to relink these manually to keep things in check. You can replicate this if you duplicate a MetaHuman blueprint for example. You'll see that the skeletal mesh components are all decoupled but still visible in viewport.