According to my own experience with silicon pressure sensors and data sheet information, I don't see why the sensor should have mB orde of magnitude short term uncertainty. The sensor will expose temperature drift over full temperature range in several 10 mB order, also a mB range pressure hysteresis according to the datasheet. But under constant conditions (thermal equilibrium) pressure reasings should be constant as well.
You didn't tell about the measurement conditions, but if they have been fairly constant, I expect amplifier noise and limited ADC resolution as dominant source of uncertainty.