Those are classic stress fractures. Excess stress causes the glass to break free of the epoxy leaving white voids.

They must be removed by sanding or removing the glass with a heat gun.

You said you were glassing a wooden car. How thick is the wood?

Fiberglass does not work well on heavier, 1/2" plus sections of wood. Glassing only one surface, say the exterior, lets the interior move with changing ambient changes in humidity.

Wood moves, glass doesn't, so you get stress fractures.

Rob