Thanks! Yeah you can't place blocks if they would make it impossible for the enemies to get to your base -- there has to be a path. There's currently a bug where the Bubble Traps count as walls too, so that makes the block placement a little confusing. I definitely just didn't have time to make a real tutorial or give the player on screen cues for block placement, but that's gonna be added soon.
I actually have a lot of other features that are close to being done already; I just had to disable them for the time being to keep the jam submission easier to understand. There will definitely be more updates soon!