please write us at least the v-ray version.
which lighting system are you using?
what kind of Gi are you using?
I assume is a global illumination problem.
try to make a render region in one of those points:
primary bounce, brute force
secondary, light cache
Vray 3.4 b2 Beta with sun and light dome…
First I I would exclude a GI problem.
you can put the brute force in primary and secondary bounces, and make a little region render exatly where you have the problem.
Edit: light leaks? Move the objects with a small gap above the ground.