Originally Posted by BubbleheadMd
Whether T-ball style or not, it sounds like something was not properly seated, and popped into place during sailing, especially based on the OP's insistence that all tabbing and chainplates are solidly intact.
BTW- any rigging that is "tight as a fiddle string" is TOO TIGHT. That's a good way to wreck a chainplate, or tabbing or induce "hogging".
"Tight as a fiddle string" Figure of speech...simply to say that the uppers were still tight. Only the lowers were loose. Also forestay and backstay were still tight.
Side note: When the chainplate pulled up through the old (waterlogged) bulkhead both upper and lower shrouds were equally loose.