I certainly don't have definitive answers, Kazmi, but I am hearing two recurring themes when experienced soapers talk about crackle.
One theme is that obvious crackle seems to be strongly related to using titanium dioxide. I don't know if TD just makes the crackle more obvious or if it can actually trigger crackle in recipes that might not crackle without TD. Some of this connection of TD with crackle might be that folks are putting TD in their soap batter before it is fully wetted. Several people say they mix TD in water, glycerin, or oil and let the mixture stand for awhile, even overnight, before using it. Oil-soluble TD versus water-soluble TD might also be a factor, but I'm not sure which might be less prone to crackle.
Someone commented that there was very little talk about crackle just a few years ago, and the commenter thought this issue is discussed a lot more now. I wonder if perhaps that's because people are using TD more often now to make the fancy swirled and brightly colored soaps? I don't have a way to know that, but it seems like a possibility. Maybe someone who has been soaping longer than I have can comment.
Another theme is that crackle is more common in soaps made with palm oil, which can have a high stearic fatty acid content if it is not well mixed before use. Some thoughts people have about using recipes with large amounts of palm include:
mix the palm thoroughly before measuring it to ensure the oil is consistent
keep the batter temperature warmer -- 110-115 deg F (43-46 C) -- rather than soap at room temperature
reduce the palm content if crackle is a persistent problem (one person was getting crackle with a recipe that had 70% palm and eliminated crackle by going to a 40% palm content)
use as strong a lye solution as is reasonable, rather than stick with "full water"
and, yes, another suggestion was to avoid gel
Just my thoughts and observations -- I'll be curious to see what you all think. I rather like soap with crackle/stearic spots/TD streaks/snail trails/mottles or whatever you want to call it.