Depends on the map.
The formula for score calculation
per note is as follows:
Score = Hit Value + (Hit Value * ((Combo multiplier * Difficulty multiplier * Mod multiplier) / 25))
That means if I'm at 300 combo and I properly hit a short slider this will give me 2 combo and a total of
300 + (300 * ((299 * 5 * 1) / 25)) + 30 + 30 = 18000 points
The +30 at the end are the individual scoreaddition from sliderstart and sliderend.
If you get 2 combo through 2 circles though it adds up to
300 + (300 * ((299 * 5 * 1) / 25)) = 17940 points for the first and
300 + (300 * ((300 * 5 * 1) / 25)) = 18300 points for the second circle
which obviously adds up to more than the slider.
tl;dr depending in which part you missed, you might have got more actual score-relevant hits for your high combo than in the other attempt.
Refer to
https://osu.ppy.sh/help/wiki/Score#score for background on score calculation.
