I would guess that the rocker contacts the spring retainer at or near max lift, pushing on the retainer and unloading the keepers, allowing one of them to come out. You are extremely lucky.
Yep.
You lead a charmed life........that could have been real ugly.
I think a lash cap might be a better fix.....it will raise the rocker another .060 or so off the retainer and open up the gap between the two , though raising the shaft won't hurt either.
Maybe a combo platter to maximize clearance ?