«The 4130 since 2019 sometime, uses the same balance as the 9001 skydweller. It has a different shaped overcoil, and under the 4130 balance bridge the coils can get tangled if the movement received a sudden shock.
Its an easy fix for an on site watchmaker. Rolex has come out with a "hotfix" for those affected hairsprings and since changed the shape of the curve a bit.»
https://www.rolexforums.com/showpost.php?p=12853975
