Hello there!
I just switched to 5.1 in order to try out some nanite things (went from 5.0.3) with foliage.
My basic setup is a Landscape material with the Grass Node. When I use a RVT to get the color for each strand, it seems to instead sample from the tile, rather than by strand.
Here is the my grass material. (I also tried (0,0,0) vector with a transform from Particle and Instance Space to World Position, same result).
And this is how it looks like with nanite enabled:
You can clearly see the squares in the foliage. If I turn off nanite, it works as expected.
Is this a bug or how can I sample per instance?