[Pardiso] high residual for symmetric indefinite system after schur complement 

I'm trying to use Pardiso to solve a Stokes problem using weak galerkin finite element method.

All matrix and code are attached and tested at MKL 2019.5.281, Visual Studio 2019, WIN10

The linear system is a saddle point system which can be solved in Full sysem or Schur complement system. Both linear system are symmetric indefinite.

//2nd order FEM with 384 tets
//System1. Full system, where u={u0,ut,v0,vt,w0,wt} and u0,v0,w0 is not shared by neighboring element
[K  G * {u = {b_u
 G' 0]   p}   b_p}
system size = 4080 x 4080

//System2. Schur complement , where u_bar={ut,vt,wt} as u0,v0,w0 is eliminated
[A  B * {u_bar = {b_u
 B' C]   p}       b_p}
system size = 2640 x 2640

left: Full matrix                                       right: Schur complement matrix

Obviously, System2 can save a lot of memory for a large problme.

Q: I can use Pardiso to solve the System1 very well (residual = 1e-16).

     But When I solve the System2, it returns the very high residual (1e-2 -> 1e4). 

     Any suggestions to solve this symmetric indefinite system?

I already tried the solution of setting following iparm but it is not helps

 iparm[9] = 8;       
 iparm[10] = 1;       
 iparm[12] = 1;