Steven C, what you are doing is exactly what I would be trying.
One thing that might make a difference, there are two general methods of chitting, first method is a few hours soak, followed by leaving between layers of damp kitchen paper in either a container, or a plastic bag. Second method is following the soak, just place them in a container with maybe 1/4 teaspoon of water in the bottom, no kitchen paper. I find that second method works a treat for squashes and cucumbers. Just the slightest bit of heat helps as well.
If you are doing that, I can't suggest an improvement, and IMO it is likely the seed. Best of luck getting it sorted out.