[1.1.1] Disappearing trees

When I have a small gap in my layout, I tend to put a tree there, if it fits. I’ve noticed that sometimes the trees just disappear. One spot in particular near my school has only a very tiny area where the tree placement square turns green. I’ve planted probably 4 or 5 trees there now, and every time it has vanished the next time I checked.

Similarly, I surrounded my temple with juniper bushes. But I just noticed that a couple of them in the middle have vanished.

The 5 gold planting spots in the image below mark where my decorative trees disappeared.