RE: What could I have done?
What a heartache...of course, two hundred and fifty yards is no chip shot but I understand your chagrin.
I haven't encountered that problem with quality scopes (which you possess), but my binocs always let me down under similar conditions...can't afford $500.00-$1500.00 for the good ones. Perhaps a seal broke? In any event (no consolation btw), demand Leupold replace that scope!