Why does this kind of broken surface appear when passing UV, do you know what causes this?

this appears when it is a model whose uv has been deployed with another software, like maya or 3ds, then opened with blender. You must also switch to "face-select" mode, then recreate the seams with the "seams from island" option.

Look like some shared vertices were welded. As @valsdieudo said, you will have to select the faces and rebuild them or redo the UV.