Hi @javier I have some bad news for you,
Firstly, It appears that Unity's built in renderer does not support catching shadows on transparent objects. The shaders that catch shadows render opaque with a transparent blendmode, but they still use the opaque render pass. This results in Magic Leap 2 capture to render the occluder incorrectly.
In summary, rendering shadows on occluder meshes is not possible when using Unity's built in render pipeline. I have reported your use case and this issue to our voice of customer team.
Secondly, we are looking into the issue with the opaque object capture right now. It looks like our Mixed Reality Capture technique and Unity's Standard render pipeline don't play nice together. If you change to URP I have a shader that would work 
, I will let you know as soon as I have more information.