Definition of "flabbiness"

There were two, or perhaps three, flabbinesses of style which (in your work) amazed me. Am I right in thinking you were a shade bored over the last chapters?

April 1891, Robert Louis Stevenson, letter to Edmund Goose

Woona had silently and swiftly backed away; and her ebon face, Ursula saw, had changed into leaden flabbiness with some horrible fear.

1907, Barbara Baynton, edited by Sally Krimmer and Alan Lawson, Human Toll (Portable Australian Authors: Barbara Baynton), St Lucia: University of Queensland Press, published 1980, page 279