The fact that it only occurred in one spot usually means the glass if fine. 99% of the time its one of two things. The viscosity is to high (thick). It could be that as you work, the areas that you first glass get the freshest and most liquid of the epoxy and later as it starts to thicken a bit, that gets used in more time consuming areas. The thicker epoxy doesn't wet out the glass as easily or as well. Second, not only is the epoxy getting cooler and thicker, but the glass gets starved a bit because its not on a flat area where you can really give it a liberal coat. You coat it, it wets out fine but later, fibers of the glass suck more epoxy and it gets dryer and a bit starved.

When I glass, I heat my epoxy in some hot water and try to use it quickly and on corners, I brush on liberal amounts because later I am squeeging off excess anyhow. And if the room is warm too, it helps. I've had it happen and once I started to pay strict attention to having very liquid mixtures, I never have it occur any more. It's quite noticeable how much more liquid your epoxy is when warm. it kicks faster but you learn to work fast. I have even added a tiny bit of alcohol to a mixture to thin it a bit. Like a quarter teaspoon to 10 ozs.

Sometimes when I do the bow and other tougher areas, I lift the glass and paint on some epoxy on the wood and lay the glass down on it and that helps too.