Can't Recognize Parameter Value

Hi, Guys.

I have a Hexa-Copter which is setted Firmware v3.5.7 and tested all the part what I want three months ago.
After the all test was ended, I kept the Hexa-Copter(I have not turned it on for three months).
A few days ago, I turned it on to check it out. I got a message that ‘Prearm:Compass not calibration’ on my GCS(Mission Planner), As if it were not set. So, I checked the parameters about compass(it was fine on the parameters list and compass values ​​in the initial tab)
After That, I reinstalled firmware and overwrote the Full-Parameter which downloaded on that day.
But, Hexa-Copter flew unstably like the PID value was not calibrated.

What happened to my drone?

I tried to find the cause, but couldn’t find until now.
I suspect that there is data corruption in the FC’s storage.
Do you know where to check?