Hi, Federico,

        There are two reasons:

1.If I use CG_MOTION for fluid_2 and fluid_3, too much surfaces I must set as rigid body in dynamic mesh, as shown in Figure 2;

2."Warning: multiple subdivision required on zone 23. Subdivide using Constant Ratio"

and "negative volume" error will pop up, as shown in Figure 3.

Figure 2

Figure 3