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This is my Echinocereus rigidissimus rubrispinus. It's having a growth spurt but I'm a bit concerned that no spines are coming through, except for at the crown. Is this a normal growth pattern?

This is not normal. My suggestions:

More sun

Less nitrogen from soil or fertilizer

Something happened during winter rest. Maybe it spent much time in shade. Don't worry this spineless belt will not be very wide and many cacti can grow additional new spines.

Thanks, guys. I bought it last year from a reputable grower, but at one point it was plagued by mealy bugs, which I treated with methylayed spirits. It seems clean now. It's been out in the greenhouse over winter and is now getting plenty of sun. It's fed with the same stuff all my other cacti get and everything else is growing splendidly this year.
I'm inclined to think maybe the stress of mealybug treatments has caused this. Hoping it's just a blip as the top is sprouting reasonable spines now. I'll report back in the autumn with an update.