Hello,

The main model (big piece) is broken(naked edges),.. basically, it is not a solid, so any booleans you make to that will give an unexpected result. With that big piece you can "separate" and then "join" the surfaces back together which will make it a solid.

When making a lot of booleans sometimes the model can become broken, I always check during such to check if the model is still a solid. To do that, you can set up a shortcut key to select solids:- the command is:-

script:moi.geometryDatabase.getObjects().getSolids().setProperty( 'selected', true );

You can add the command in the shortcut keys, and add which key you want(not already in use)