Hi Carlo,
Yes, I see it now. The KML labels are being partially occluded by the terrain, as you observed. A way to resolve this is to disable depthTestAgainstTerrain
:
viewer.scene.globe.depthTestAgainstTerrain = false;
You can see that in this Sandcastle.
There is some additional discussion in this forum post and in this GitHub issue, if you are interested.
Thanks,
Matt