Often times we speak of the sprue puddle "hazing over" when the alloy starts to become solid. Looking at the bullet bases, are we seeing some pin hole cavities or is that just the lighting? Also, some appear to be cut and some appear to be torn from the base. That suggests being inconsistent in your timing. Not a problem for me personally, as I would size/lube and shoot anyway.
I do not understand your comment that the slow cadence did not allow the mold to get hot enough. The mold and sprue plate should have been too hot and starting to cool down as you match the cadence. The important thing about the casting cadence is not just the fill, cool, cut, cool, dump, but the immediate refill, cool, etc. If you are delaying in refilling the mold it will cool excessively and give wrinkles. Still not sure why the mold is not releasing more easily though.
You are in So Cal so it can not be that cold, but perhaps you are casting in a breeze and that is robbing the mold of heat a lot faster than casting in a calm area with sufficient venting. Are you running the pot stop valve wide open for a quick fill, or throttled back so you make soft serve ice cream cone type wrinkles. Showing the problems can sometimes help clear things up.
About to the point of suggesting just smoking the mold with a Bic lighter and see if that will allow easier bullet release. Is this your clip on wheel weight alloy with tin added? What is the mold nominal weight and what is the as cast weight?