OK. I guess I got it ... The option: sceneView.allowsCameraControl = true (which allows the control of the camera by the user) is definitively incompatible with the camera tracking through the "Look At" constraint (which makes sense). Setting the option to false solves the issue.

Fine! I was guessing an emoji was a sort of predefined 4 bit integer ... which obvious it isn't. But things are clear for me now. Great. Tanks a lot!