Never used that brand of resin, but there can be issues with the whities when using epoxy over doark colours.
a picture would help. what stage of glassing did it appear, did you notice it before or after sanding?
Blush: is a milky flim that forms on the surface if the temprature was too low when you glassed, it will stop subsequent layers bonding but you can sand through it.
Crystalization: is worse, lloks like white crystals that forms on the surface if the hymidity is high or moisture settles on the surface while it is curing (like for dew)
Ghosting: Most likerly cause of the whities is from overworking the resin and cloth, and frothing the resin up most common around the lap line where resin is pulled off the flats to saturate the hanging cloth. basically los of small air bubbles traped in the resin. You can stop this by heating the resin so its less viscous. or going over it with a heat gun this not only heats the resin but also breaks the surface tension in a hot coat to release traped air bubbles.
Out gassing: You also get problems with out gassing from the blank, espcially with woods, did you seal the blank with a sweet coat before glassing? avoid this by sealing the blank and glassing on a falling temp, the blank will contract and suck resin instead of expanding and blowing gas.
Also If you didn’t seal the bland and the wood was very pourus it could have sucked you lam dry. id you still seeing the texture of the weave after a fill coat you will probable be able to sand with out actually hitting the weave, sometimes with epoxy the resin with sort of confortm the the texture but still give you a thickenouth layer to sand it out, if not then jsut another coat of resin with solve this.
Of course is could be as simple as you’ve sanded too far and hit the weave of the cloth, if your seening the checkered patter after sanding but did not before than this is the best bet.
Or there could be a problem with the oils in the would and that brand of resin.
It could also be bad cloth, my fin halos and leash loops would always come out a little milk, not the real clear like using poly, skratched my head over that for a long while, tried every trick in the book, eventually I ran out of roving. New roving no more whities.
Could the cloth have gotten damp or been sitting around for a long while and soaked up moisture in the air?
So in summery,
*pre heat the resin a little before adding the hardner
*glass on a falling temperature
*mix resin slowly to avoid loads of air in the mix
*give the resin time to soak in to the cloth, don’t over work it
*saturate and fold laps before pulling resin off the flats
*if your sanding the hot coat and start to see a checkered patter you’ve hit the weave, don’t sand any further.
- sand off any films that form on the surface( between fill coat and gloss) 220 or a green scotchbrie pad, alocohol rub, water and detergent, and let dry thoughly before going to next layer,
Hope that helps