[PyMOL] rigimol (morph)

Dear all,
I am trying to morph two protein-protein complex pdb files.
Everything looks fine but somehow during the morphing the complex structure
is also bouncing up and down instead of a morphing at a fix large catalytic
reference domain of chain A.
If I only use chain A of the complex it morphs perfectly, somehow including
chain B makes things complicated.
How can I morph these two pdb without extra bouncing.

With my best regards.

Hasan