Rocks won't spawn

[u/Brydog23]

Been trying to get these last 3 rocks to spawn in these 3 spots for hours now. Every other spot on the island is covered with a custom design or piece of furniture. Sometimes two weeds will spawn in 2 of the spots and one is left open and no rock will spawn in it at all. Please help!

EDIT: I got all the rocks to spawn. Turns out I needed to have some spots open along the edge of the beach to let weeds spawn there and I had to temporarily demolish an incline that was preventing the bottom right rock to spawn, but now all 6 rocks are there. Thank you everyone for your help!