If a disabled object (i.e. setEnabled(false)) is cloned, its children seem to be cloned with the wrong enabled state. Subsequently calling setEnabled(true) on the original object will show the object and all of its children, but calling setEnabled(true) on the cloned object will not enable the children.
Demo: Babylon.js Playground
Expected result: two models would be shown, both the original and the clone.
Actual result: only the original model is shown.
Some visibility info is logged to the console in the demo.