Be sure you any custom profile you made or downloaded. I confirm the configuration for the A310 in the GSX internal database is as follows:
Cargo 1 ( front ), will use the AKE ULD
Cargo 2 ( rear ), will also use the AKE ULD
Main Cargo ( bulk cargo, last door in the back ), "should" use a BELT loader.
This means, if you have Belt loaders on cargo doors 1 and 2, you are not using the current GSX internal config.
However, I now see there's a problem with the Bulk door because, even if it was configured as a Belt loader, repurposing the MainCargo as a Bulk loader doesn't really work, because GSX assumes the Main Cargo door is always a true "Cargo" door, so it will always try to use a Cargo loader.
This is not just the appearance of the loader itself, but it also affect the path taken by the carts, which is oriented opposite to the other baggage carts, and even if it wasn't, there's just not enough space to fit (any) loaders on both cargo doors AND a 3rd loader on the bulk door, the animations and the approach paths are just not made to have 3 loaders on the same side of the airplane all working at the same time.
If you like to see baggage and use the bulk cargo door, the only sensible way would be moving cargo 2 to the bulk door position, and removing the Main Cargo door altogether, so you'll get an ULD with AKE in Front, and the Bulk loader loading bags in the Rear using the bulk cargo door.
I think this is the configuration that makes most sense, so it should be the new default.