The leaking is caused by the cascaded shadowmaps. At one point, dynamic whole scene shadows from the movable directional light switch from the first cascade to the second. That cascade has the same resolution as the first one, but since it has to cover more geo with it, the resolution gets worse, thus the edges of the shadows become so soft that you see this leaking effect.
There is only one way to fix this properly without sacrificing draw distance for shadows or adding more cascades (which is more expensive and you should not do it) and that is increasing the resolution of the cascaded shadow map. Standard is 1024 which is extremely low and actually not really usable for dynamic setups.
Put r.shadow.maxresolution 2048 or 4096 into the consolevariables or type it into the command line and you leaking should be gone 