Why gltf model no activeAnimations by scene.primitives.add

Cesium1.114.
i have a gltf/glb model with animation In Blender,when i add it by use “viewer.entities.add”, i can see model animation , but when i use “viewer.scene.primitives.add”,the model dont show animation ,there someone said use “model.activeAnimations.addAll()”,but it doesnt work,length is 0,someone know how to useful,help please.