You observe that the kernel_task process is reaching high CPU usage.
When the kernel_task process uses a large percentage of your Mac CPU, it's because the device is overheating. When the device overheats, the macOS halts CPU power from other software and "reserves" it under the "kernel_task" process.
The OS does this to prevent other software from exacerbating the heating problem. This operation is a function of the MacOS and is not the result of any actions of the Symantec Endpoint Protection software.
For more information, see: https://support.apple.com/en-us/HT207359