you have to take into account, that FreeCAD exports only selected parts.
So look at your object browser and select all parts, that make up your solid - selected parts show up in light green.
When your whole part is green, you probably have all relevant parts selected.
But be careful, not to select subparts too.
So for your cut, you'll find a "cut" entry in object browser, which has 2 subparts. "cut" should be selected, the subparts should not be selected.
Ctrl + mouseclick is your friend