I can't place Exotic Wood Tree Nursery at any archipelago island.
Here are two screens (below).
I previously cleared Black Castle (4x4) from this area. Woodcutter (2x2) can be placed, Exotic Wood Tree Nursery (2x2) can't.
Is it a bug or Exotic Wood Tree Nursery can be only placed at the main island?
BTW - brillant answer from support after I sent screens you see: "According to the screenshot, it seems that you were trying to place the building in a location that has not enough free space. I suspect that it may have been the source of the misunderstanding."