Is it absolutely neccessary the dishes to be rock rigid still¿, could a little moving because of wind to disturb the link¿
Yes and yes.
The signal drop from -80dbm to -50dbm is a huge difference.
So it seems your antenna goes wherever the wind goes...
The link HAS visual contact, but the Fresnel zone area is not totally clear
Since beamforming is used in the 60GHz models i dont think that this is a real problem.
Also the radiation pattern is :
< 1 degree single pattern and full span 3 degrees over horizontal and 3 degrees vertical plane
The radiation pattern is so narrow...
As the wiki suggests :
LHG60 devices require very precise alignment in order to get best performance in higher distances.
So imagine what can happen if they move because of wind...