66AK2H06: DDR3 bit error

Hi,

My customer is using 66AK2H06 and reported DDR3 bit error on their board.
The error occurs depending on Read leveling results.
If the result is ~40, there is no error.
If the value is ~90, the error happens.
I think the value should be ~40 for correct operation for the byte lane on this board.

What is potential cause(s) the read leveling results varies even on the same board?

Please see attached DDR3_biterror_161117.xlsx for details.

Thanks and regards,
KoTDDR3_biterror_161117.xlsx