I have tried all different kinds of settings when hollowing the pieces. 100% precision, 0% precision (this works better), 2 mm wall, 3 mm wall, even up to 4 mm, doesn't fix the fragmenting.

Here's what it looks like for me:

https://i.imgur.com/GsKLgxE.png

And it causes there to be a lot of overhang and islands being formed and unsupported. I feel like it should just be a gradual slope from the floor to the wall to the ceiling no?