Bootloader burnout

The bootloader was frequently burned out on my cube black. After rewrite bootloader using ST32 utility, the official firmware works, but when I update my customized firmware , the cube can’t be started up. I tried to update my paramet list and reset default parameters after install official firmware, then I can update my customized firmware, and the cube can start up.

I don’t know what is occurred bootloader burnout.
The cube is connected CAN, I2C, aux, serial devices.

Any advise, very appreciated.