Some grass turns black in light probes

Hi! I'm trying to bake some light probes to light grass (painted as terrain trees in HDRP) with GI. However, some of the grass clumps turn black, even though it connects to probes that are receiving light.

Also, if I delete or paint out the black grass, some other surrounding clumps turn black instead. Something else of note is that, when erasing grass, surrounding grass also changes shade, with each erase. Like the instances are being shuffled in some array registered to the probes.



Anyone recognize this?

Unity 2019.3.0f1
HDRP 7.1.6

 

I got it - the setting for "bake light probes for trees" in the terrain settings means it generates an entirely new light probe for each tree/grass instance. Not that it uses your pre-placed light probes. This makes sense for actual trees, but since you also have to use the tree system for grass in HDRP, it breaks.

In other words, it somehow compounds the terrain light probes on top of your own light probes and gets the wrong values.