I am debugging a power amplifier circuit and trying several capacitors values to fine tune the design to meet the frequency response specifications. All the 0603 and 0805 ceramic capacitors are experiencing the following issue:
I measure the capacitor (this one for example) using this digital LCR meter which reads 360nF (typical value 390nF with 10% tolerance). When I hand-solder the capacitor, it reads 420nF in-circuit, and when I desolder the cap, it still reads 420nF. What caused this big increase in capacitance?!
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.