GIZMO is not manifestly conservative
Manifest conservation of mass, momentum and energy was consciously broken in !470 (merged) to make the GIZMO scheme more similar to the other SPH schemes, and because manifest conservation is not currently possible for interactions between active and inactive particles if the particles are not on the same MPI node. For some applications, manifest conservation could however be essential, so it would be a good idea to re-enable this or at least provide a GIZMO version where manifest conservation is possible.