Hi @VictorDiaconu
I hope you are doing well!
So, If you try to trigger the mass erase once again with J10 installed or releasing ISP button after reset the process fails again?
From my experience, you can set the MCU into ISP mode ( by installing J10 when the board or releasing ISP button after refer ) and then trigger a mass erase. However you do not need to set the MCU into ISP mode to trigger a mass erase. Having the MCU into ISP mode, helps to recover debugger connection in some cases, see Regainning debug access to target MCU. After the mass erase was succesful, you may want to uninstall the J10 to trigger a debug session.
Also, to recover the MCU , we can try by using Flash magic Tool , J-link commander or even an external debug probe, if required we can check them.
Regards,
Diego