It may have to do with your graphic settings or your pc rig. Sometimes smaller things like foilage despawn or “disappear” when you have low graphical settings or render distance.
Thanks for the suggestion, but that would only explain distance culling. I can move further to a tree though, and it still disappears, if I move away too far from some certain point in the level (I believe it is the middle of the level, but I don’t know how to verify that).
Also, as far as I can tell it only happens in this particular level. Although it is by far the largest I’m working with, so that, too, is hard to verify.