Hi Dave_C,
Have you contacted Habitat to ask about a warranty replacement?
Even if you don’t want to use it any longer it seems that your mattresses may be defective (or used a bad batch of foam) and a phone call and a warranty claim would certainly seem to be worth it. If nothing else you could sell them or use them as a spare. If I was in your shoes it’s the first thing I would do.
I agree that some of these “anomolies” seem odd to me as well although a material that softens will do so under the areas where they are most subject to constant compression and greater weight. I’m not sure which version you bought but I believe their top layer is N1 which is the softest 100% natural Talalay that Latex International makes and would be a less durable version of latex than the Talalay blend (see post #2 here). Assuming that the materials are what they say they are, using N1 as a “standard” comfort layer may not be the best design choice. Their base Dunlop layer is apparently 26 ILD which is also on the soft side for a support layer (and this could also be the defective layer) and the overall softness could contribute to a feeling of “roll together” in the center of the mattress for some people even without the latex softening.
In any case … I hope you call them and see how they respond to a warranty claim.
Phoenix