Could just be a bad cap. Were the bottles you took to the party chilled as well? What seems to be enough carbonation at 55F can be flat from the fridge. I have this problem every time I swap the soda water kegs. I pre-carbonate at room temperature, but once in the fridge it takes a day for the pressure to come back up.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
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