Related to: Q19854: Invisible plant and Q22226: Found new plants with fancy invisibility powder
Since the latest update to the Experimental release, a number of large, invisible mushrooms have appeared in the pink/red bamboo area in the central part of the map.
You can see the outline of these while holding the chainsaw. They can also be removed using the chainsaw, or nobelisks.
These make it very frustrating to navigate the area using your explorer (or other vehicles), because when it hits one of these invisible mushrooms, it will twist, flip or just stop dead. You cannot drive through them. There are a LOT of these invisible mushrooms, so driving around is actually quite difficult.
Before the update, this area did have a lot of these giant mushroom structures, and I had spent some time removing several of them. I cannot say, however, whether or not the invisible ones are the ones that I had previously removed.
As you can see in the image below, there are also some invisible mushrooms right next to visible ones: