Last Shelter: Valley Defense Battle – not enough sites

There is a new minigame in Last Shelter Survival and it's called Valley Defense Battle. It's a pretty straightforward game, but there is a problem that you might encounter around level 100-110. All of the sites for new buildings become full and you cant create new ones. It's probably a flaw in the design, but I'm not sure.

The trick is to drag an existing building out of the site and while still holding the building outside, you click to create a new one. That way, the building you're holding will get destroyed and the new one will appear.

I also found a video on YouTube that I will link, it's the only one I found adressing this problem:)