I have seen it a more than a few times. Must not let IFS fully droop when torquing the bolt down.
IMO the shock was fully drooped and the spacer was in direct contact with the side of the cup.....then torque was applied causing them to hit each other............then you notice it and say "how did that get loose and damaged"......the real issue is it never got tight because it was at such a severe angle it impacted the side.
Thats my guess after seeing this happen many times. Could be wrong......