I think all string will move . If they didn't move you would never break a string. No movement, no friction sawing action, and no breakage. String could also move more because they were tensioned too fast, clamped too soon, strung at too low a tension, or any combination of those. Soft string tends to have move friction and move less but when they do move there is more friction and they tend to stay distorted. I would think a smooth string would be better.
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