VectorPyCoefficent invalid size causing crash about pymfem HOT 5 OPEN

class StrainVectorCoefficient(mfem.VectorPyCoefficient):                                                                                                                             
    def __init__(                                                                                                                                                                    
            self,                                                                                                                                                                    
            dim: int):                                                                                                                                                               
        super(StrainVectorCoefficient, self).__init__(dim)                                                                                                                           
        self.dim = dim                                                                                                                                                               
        self.u = None   # displacement GridFunction                                                                                                                                  
        self.grad = mfem.DenseMatrix()                                                                                                                                               
       
   def SetDisplacement(self, u: mfem.GridFunction):
        self.u = u

    def Eval(
            self, v: mfem.Vector, 
            T: mfem.ElementTransformation, 
            ip: mfem.IntegrationPoint) -> None:
        self.u.GetVectorGradient(T, self.grad)
        self.grad.Symmetrize()
        
        size = self.grad.Size()
        # Set the principle strains xx, yy, zz, xy, xz, yz
        if size == 2:
            v[0] = self.grad[0, 0]
            v[1] = self.grad[1, 1]
            v[2] = self.grad[0, 1]
        elif size == 3:
            v[0] = self.grad[0, 0]
            v[1] = self.grad[1, 1]
            v[2] = self.grad[2, 2]
            v[3] = self.grad[0, 1]
            v[4] = self.grad[0, 2]
            v[5] = self.grad[1, 2]

        return v


def get_xyz(c, mesh, gf):
    _, elem_ids, ips = mesh.FindPoints([c])
    c = [gf.GetValue(elem_ids[0], ips[0], i) for i in range(4)]
    return c

dim = 3
strain_coef = StrainVectorCoefficient(dim)
strain_coef.SetDisplacement(x)

vector_space = mfem.FiniteElementSpace(mesh, fec, dim)
strain = mfem.GridFunction(vector_space)
strain.ProjectCoefficient(strain_coef)    

print("data")
# WARN: if sleep is lower than 3 it crashes prematurely
sleep(5)
print("Strain", get_xyz((10, 0, 5), mesh, strain))

# NOTE: Complains about destructors missing
del strain
del strain_coef