There are a few dead ends that aren't obvious so I flew into them a few times.
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The main problem is the tunnel. (Can't post a picture because of size limit but Just go right near the floor and you'll find it)
It is also a little annoying that you can't tell which walls you can go through and wich ones you can't.
From what I can tell the red ones are passable and the black ones are sometimes. That doesn't help the issue.