Found it. Bot's that arn't seeing anything are being struck blind by an invisible undead zombie shape!
I am almost positive you have added and then deleted some shapes in this sim, leaving the shapes array with holes of non-existing shapes. I have a bug in the routine that checks to see if a shape blocks a bot's vision of what's on the otherside. I fail to check if the shape exists! Thus, your bot's vision is being blocked by shapes that once existed but no longer do.
Already fixed for the next drop. If you want to work around for now, delete all shapes then add back the ones you want. Deleting them individually is what makes them zombies...