Ceramic capacitor value changes after soldering!

The only clue I can find might be this: -

It looks like you are seeing a +16% shift in value and X5R is not known for the greatest dielectric so this may be counted as some form of initial aging due to soldering. After all, it started about 8% down and it's gone 8% over. I'd expect X7R dielectric to be better (stabler) and C0G/NP0 to be better again.

Capacitor aging, including capacitance shift specifically after reflow is apparently an issue. See https://youtu.be/ZAbOHFYRFGg?t=675 (James Lewis, Kemet presented a talk at a Supplyframe Hardware talk: They're JUST Capacitors)

Change is regardless of whether power or temperature as long as you are away from curie point of the material.

The shift "resets" if the caps are reheated.