Hello Pinout,
How did you read the Device ID, please use IAP/ISP Read part Identification number.
IAP command:

There is demo under LPCopen, falshiap_flashsig, you can directly refer to it.
/* Read Part Identification Number*/
command[0] = IAP_REPID_CMD; /* Read ID command code */
iap_entry(command, result);
DEBUGOUT("Part ID is: %x\r\n", result[1]);
If want to use ISP command, enter ISP mode, and using Flash Magic to read.
BR
Alice