I re-tried lock, but could not.
At first, I adjusted the offset of servo to set the monitored error signal to zero.
Also I minimize the gain of servo.
I tuned the laser frequency around the resonance, and turned on the integrator.

I tried several times with different conditions (inverted or not, and so on..), however, could not lock...
There may be some problems such as high finess, large gain, etc...

Actually, the efficiency of laser PZT is 50MHz/V, and the slope of error signal is 4.2e-7V/Hz.
Therefore, it needs to optimize the gain of the servo.