I've got a catalog at work that is all about floor repair & maint products.

Gypcrete is not a verys trong product but it is widely used in multi-unit const
fro fire & sound proofing.

If installed (mixed) correctly it shouldn't bust up like that but once it does
you've got somewhat of a problem on your hands.

Epoxy or polyester resins won't be cheap; depending on amount required you
might be in the $'s per ft^2 range.

Short of complete R&R you need something to penetrate & consolidate the
material.

All depends on cost........R&R might be cheaper