Looks like plywood stitch-n-glue? The pictures, are these only on the hull bottom? Is the hull bottom flat?

Yes, Pygmy Tern 14. Hull bottom and sides. Not flat, shallow V

How was the inside sealed? Epoxy? Epoxy & Glass? Epoxy, Glass plus one fill coat?

Standard Pygmy layup: 6oz glass inside and out. Surface is smooth inside and out, you can't feel the weave.

If the interior surfaces have not been sealed to balance the moisture permeability of the exterior you have a leak in your ziplock bag. I'm going to guess moisture has absorbed into the plywood causing more expansion contraction of the plywood core.

Moisture and flexing over time create damage.

There is no discoloration indicating moisture under the glass. Also the tiny cracks are only on the outside of the hull, not inside and not anywhere on the deck.