So I found out that RP_Riverden is what was causing this bug with the grass textures.

I actually have CSS installed as a *game* and not in the addon folder, so I think I can rule that out. I've thought that maybe some addon is replacing the foliage but I don't have any foliage replacement addons.

Just gonna jump in on this but you might have..
1. A mod/map that unintentionally replaces the foliage.
2. You have CSS or other games installed on your addon folder rather than it being mounted.
Make sure you disable all your addons with the exception of the map and enable each addon page on your game before loading the map.

I have. Not sure why this happens.

in my game they look completely fine. maybe try verifying your game files

i have no idea why it looks like that