Hi. I previously owned a JS100 in black had got this problem so I changed it for a new one even I solved it later.
The sipderweb-alike cracks are simply like the nail scretches so I have the guitar body polished time to time and the cracks disappeared gradually. In fact, my problem was not that obvious, it just apperaed under strong light. Anyways, there's a little trick when you do polishing. When you finished putting on those polish stuff, you put the guitar body in front of the air conditioner to let dry, it let the extra amount of the polish stuff dried in solid and you use a fine clothe to clean it thru grain. If you do this from time to time, the spiderweb will be gone, the denstity of the guitar body will even become higher and make a better stuatin.