Larian Studios Forums Divinity - Original Sin Divinity - Original Sin - Enhanced Edition Try to sell to a vendor and get no gold in return

Check the containers in the characters' inventories (backpacks, etc, and there is a pouch container with the the same icon as a pouch of moondust or bonedust). It is likely gold added to their inventory is being stacked with gold in a container (possibly a crate picked up without looting first, etc).