GSX baggage loaders don't have any dependency on the *actual* cargo loaded on the airplane. Nothing in the GSX code checks the cargo quantity to know if it should stop, this is very different that, for example, the fuel.
Whether you see one or two loaders, it has no relationship with the airplane load, the only thing that controls which and how many loaders you'll see, is:
- the airplane cargo doors configuration
- the eventual disabling of a loader in a scenery customization
The actual cargo capacity doesn't affect in any way the loading process, it will only control the number of baggage/cargo carts that will be created, so GSX will assume the process is completed when all carts have passed through, what's happening in the airplane own payload is completely irrelevant.
As usual, always try with an airplane that doesn't control GSX by itself, because that's the only way to know if something must be fixed in GSX.