Possible a variation in temperature changing the setting, a leaky diaphragm in the regulator or you're out of CO2. Adjust the pressure and see where it is this evening.
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!"
"I would like to die on Mars, just not on impact." Elon Musk