This is the bug that happens when you click the same post while trying to place a freestanding wall twice. @yshan (I’m Aerietty on the Twitch chat, could finally post this like you asked!)
How I did it -
Step 1. Go to place free standing wall.
Step 2. Click + Shift spot on ground where you want to place the first post/column.
Step 3. Hold shift and place the second.
Step 4. Hold shift and reclick the first column again.
Now you can’t remove the building or even build anywhere else, or at least not use the freestanding walls at all.
Here you can see that you can’t build any new buildings after this happens.