I don’t really think these rockets are high tech enough to worry about micro cracks, these are old tech that wasn’t designed to such a precision that micro-cracks even enter into the consideration.
More likely it is going to be metal fatigue and hydrogen embrittlement.
I think the micro crack stuff is just invented fiction.
Ah, no, this is a solid rocket motor problem - it’s the same reason we had to retire the AIM-54s early. A solid rocket motor that develops microcracks doesn’t burn like it’s supposed to but tends to explode. All solid rocket motors are prone to this problem and the Strelas (from version 1 through 2M) especially are notorious for explode-on-launch when they get old.