Yeah that purple checkered grass bug has been bothering the hell out of me for months, it's broken so many custom maps. One of the updates caused this, but I don't remember which. I hope TWI will fix this, because not all mappers can fix it themselves.
Funny thing actually, I literally had a dream about this a few weeks ago. I dreamed that I was inside KF2, walking around a big custom map with so many great environments. But then, I look up to this big waterfall/cliff, and there was a giant purple checkerboard all over the cliff. I flailed my arms while yelling "TEXTUURREE BUUUUUUUUUUUUUUUGGG!!!" and then I woke up.