mpidr doesn't work for all PE

I'm trying to  get all core id for multi core on A65 in Firmware code..

mrc p15 #0, r0, c0, c0, #5

Especially, I get core id in assembly

    mov r1, #0
    mrc p15, 0, r1, c0, c0, 5
    ubfx r0, r1, #8 #8
    bx lr


core_id 0

core_id 2

core_id 3

core_id 4

core_id 5

core_id 6

core_id 7

But unfortunately core_id 1 never appears. I think PE1 is stuck somewhere but don't know inside.

Would please guide me if all core id is not working (some core id is not responding), what am I supposed to do?

Is there any way to find the reason why PE1 is not responding? how would I debug this?