Plywood floating subfloor over concrete questions.

Hello I am new here and did a quick search of this forum, but could not find anything to answer my questions.
I am wanting to know if a plywood floating subfloor should feel firm or spongy? I have a 12'x10' room that feels pretty solid but the 6'6"x7' closet seems to bounce. The subfloor is two sheets of 3/8" plywood at 90* to each other over a 6mil vapor barrier. I flattened the floor using shims and 30# roofing paper. Will this spongy feeling go away when I install my 3/4"x4" hickory planks? If not how do I address this issue? Could I drill holes where it feels bouncy and squirt some liquid nails in to firm it up underneath the plywood, or should I rip it out and reflatten then install the subfloor again?