Problem with resin eye

So I got some resin eye blanks made and I'm using them in a mask ( it's an animal but not really a fursuit).

I used acrylic paint for them and they both looked great. However, the paint on the back of only one of the eyes has started to crack.

So I went in, tried to paint into the little cracks but it didn't work. So I designed to scrub the paint back. I got to the layer that needed the most work - the pupil - and tried to paint into the minute cracks that had appeared - but the paint isn't showing up on the other side. I'm still seeing the cracks with light shining through.

As I said, the other eye is completely fine it's just one that went crazed.

Any idea what's going on and why paint isn't covering the cracks?