Hi Erich,
After soldering a brand new IC on my own board, i tried to unsecure the IC but it still failed.
Here is the pulse measured on Reset pin. It is unusual?
Does it work if you do the same thing with a FRDM-K64F board? If so, it could be related to your board layout (unlikely, but just a point to consider).
The more important thing is: have you disabled mass erase on your device (see How (not) to Secure my Microcontroller | MCU on Eclipse and Preventing Reverse Engineering: Enabling Flash Security | MCU on Eclipse ). If yes, then you won't be able to recover your device.
I hope this helps,
Erich