It even happens with like 3 layers. Which not too many layers.
Most realistic environments go up to 10-11 layers.
The problem is with the LandscapeLayerBlend node.
I am completely changing my workflow and so far I don’t have any problems no matter how many samples I use. But I still have some work to do on it.
OP are you using the LandscapeLayerBlend node too?