k...that really isn't very many instances at all (compared to 100,000) , so I would say the amount of instances shouldn't be causing the box effect...but at this point, thats the only thing I can think of right now, that maybe your gc can't handle that many instances.... (Vue just doesn't sync well with ATI Radeon)

 

what u can try is save & close Vue ...reopen Vue and create a very small terrain (100x100) ...add the same plants to the defalt terrain mat...only use just 100 instances...see if it still presents as boxes