System Information
Operating system: Windows 10
Graphics card: NVidia 970GTX

Blender Version
Broken:
2.93.3 and latest 3.00 alpha
Worked: (optional)
2.92

Bool tool addon "slice" option removes one half of the model if slice object is a plane

From default cube startup
Select cube
Enter edit mode
right click->subdivide (just to give a little more geometry)
Enter object mode
Add->Mesh->splane
Scale plane so it exceeds the size of the cube
Ensure plane is selected
Shift select cube
Select "Bool Tool -> slice"

2.92 behaviour was to split the cube in two parts (sometimes it would leave an outline of the plane as well but not always)
2.93+ behaviour is to drop half the cube

I attach a blend file of a more complex model that can be used to demonstrate this in each version of blender