What major problem did stellar models show regarding the initial shock wave following core collapse?

Answer

It rapidly lost energy as it moved outward through still-infalling layers

The initial shock wave often lost energy as it moved through the overlying stellar layers that were still falling inward, causing the shock to freeze or regress toward the core.

What major problem did stellar models show regarding the initial shock wave following core collapse?
starsupernovaexplosioncore collapseImplosion