The 120% of chain minimum breaking load requirement only applies to the design of the fairlead, chain stopper, and anchor pile.
This requirement does not apply to the shackles or H-links linking the different segments of the mooring chains. Please note that shackles or H-links designed to 120% of chain minimum breaking load might not fit geometrically due to their oversize.
The objective of the 120% requirement is that in case of a mooring line failure the connections to the FPSO and mooring pile shall be undamaged such a new mooring leg can be installed without repair.
Hope that helps.