Shadow map problem on my static mesh

hi, i am havin a problem to understunding shadow maps in unreal.
i know about how important is to create good lightmap uv but still i cant understund why this is happening.

i posted some pics about what is happening.
i checked RGB on shadowmap to make it more visible just to show what the the problem are.
What i dont understand is if the lightmap UV are bad why they work almost fine at the top of the stairs and being a mess on the bottom.(also with keeping the uv like that contiguous, i am almost seams free.)

i set up light map resolutio to 1024. and general lightmap size on 2048 on world settings.
directional and skyLight are both at stationary.(i read that like this grass is rendered more fast.)

any one can help me to understunding this?
thanks all.