Aquilo is a bit weird about the ice platforms and the tiles you need to build on top of it. There's some hidden mechanics in the game where it decides which tile to use to cover things up. I suspect setting up this test world might've bypassed something that would've not been bypassed in a regular play.
That said, I thought I knew how to trigger it (simply place a concrete tile should do it), and that didn't resolve it for me. Fortunately with little trial and error I managed to manually cover the whole place in tiles, use P.U.M.P., and get the same detached pipe tunnel as you've shown in your screenshot. So I am able to reproduce the issue with the save. 🫡
Next step is figuring out why. I've loaded up the layout in a little test-tool I made. But for some reason the resulting layout is different in the test tool then it is in the game. I suspect one of the mods in the save is altering some defaults; and the tool only uses vanilla values.
What I'm trying to say is, that it might take some digging. 😅
You mentioned: sometimes one of the pipes doesn't quite connect at the center of the layout
.
Just curious; but does that mean this is a recurring issue for you? How often are we talking about (approx)?