See also aging from Johanson Dielectrics Inc.:
“After the soldering process, the capacitors have essentially been De-Aged. Capacitance
measurements may be erratic in the initial 10 hours after testing. This is due to the initial
capacitance value, dielectric type and the time between reflow and the capacitance
measurement. For this reason, it may be necessary to wait for the capacitance to stabilize
after reflow before testing. In “High K” dielectrics, the capacitance may also appear
slightly high after the soldering process. This is normal as the capacitance is intended to
be stable after 1000 hours so that there is adequate capacitance throughout the life of the
circuit.”
Here is an additional post that may be helpful.