I can see through part of my mesh

I'm having an issue with this prop and not sure what's causing it. The support poles on the pack seem to be showing the planes behind it, but not making a solid object. It doesn't look like it's happening on the front part (not my image btw, just a placeholder while I worked). Which is confusing since the process I used to make the front display board is the exact same for the poles. If I rotate to ground level on the back I can see straight through the tubes.

Anyone know what I've done wrong here?
drive.google.com/file/d/1AkiqDpka5mhtTxcPlkVhGc5vYp3aBHf9/view?usp=sharing