I scored a nearly new Carhartt beanie there last month, same vibe.

Yeah that's totally it, you really gotta baby the bottom part lol. I cracked so many pieces before I figured out the base needs to be just as hot, if not hotter, than the rest of the glass when you're starting. My rule now is to keep spinning in the flame until the whole thing looks like it's moving as one thick, slow liquid, not just the top. If the base is stiff at all, it's just holding onto stress and waiting to blow.