I think the other guys about covered the possibilities, any of which could have been your problem singly, or in combination. Number 3 on M1919's list is a prime candidate. Depends on the actual differences between lubes, but sometimes it takes quite a while for one to "settle in" after an ammo swap. I sometimes hurry it along by running a pull-through with solvent down the bore to at least get the old lube out.
I'd go back on a still day, avoid firing while there's any wind at all (and set out a couple of wind indicators to be sure), with the ammo that did the best last time. Check the scope for parallax while on a steady rest, and focus carefully to minimize it. Be very consistent in positioning your head behind the scope. Honestly, at 24x, if it's not adjustable for parallax, there might be a lot present.
Good luck.
EDIT: Flyers, inherent in even the best standard grade ammo, make evaluations tough. The two fellow geezers at my range that hold regular "dot-shooting" matches usually use SV, which is very reliable and consistent, but still get flyers on occasion. I think DigitalDan said Euro-stuff is better in that regard.
