About rendering issue after light building

Hi everyone !

I have a model that I imported in UE4.
No problem to place it into the scene, to apply the material.
The problem comes when I build the lights. A few dark spots appear on the texture. They disappear when rotating the model.
They are always here in play mode.
I thought the problem to be linked to a missing light map.
I added it but the issue remains.
Could you help please.

Thank you very much.

PS: The attached photos show the model before and after building of the lights.