Im gona say its the chemical mix that was used to "stabilize" the Koa that may actually be the problem. Just my 2 cents here.
I have tried many "stabilized" woods from many sellers and self proclaimed wood stabilizers over the last 7 years. Most were very good or excellent. Yet there have been a couple others. Where the wood was soft and even seemed softer then it should of been unstabilized. Making me think whatever they did when they "stabilized" it was the problem. . It almost seemed to me that the chemicals or the process they used, actually degraded the wood and left it spongy for lack of a better word.