Could be genetics. Could be related to light both too much and too little can cause foxtailing. A knobby crown that's still dense and well-developed is probably too much light. If extra leafy and airy, could be too little light. And, genetics is always lurking as a cause you can't really prove with your eyes, but can be a strong possibility of being a factor, too.
Neither of these look llke 'too little' light is the cause. So, 2 options remain.
knobby hat fills in well is fine. A loose structure with a ton of lose spirals of calyxes is tolerable to unacceptable depending on severity. Can always make some bubble hash or edibles with it, but if stemmy and loose it'll be meh smoke that's heavy on small twigs and therefore harsher than it could be.
So, the first picture looks fine, the second looks a bit larfy. I'd wager in addition to potential genetic causes, these colas are getting slightly too much light at the top, and the 2nd picture might also have a genetic predisposition to it.
I've got more than 1 knobby bud this grow cycle. A couple have too much foxtailing for my tastes, but the colas are well-constructed despite a few spirals and the knobby dense ones not negatively effected. I could also cut off the skinny spirals on the couple that have them, but if they are dense enough i'll just ignore.