Why does the Intel® Arria® 10 DDR4 IP not correct an ECC error?

Resolution

A correctable bit error will not be corrected in the Intel® Arria® 10 DDR4 IP when a data mask does not correspond to a full byte (for example, a 4-bit data mask).
This is because the ECC logic can only support read-modify-write on a byte-wide basis.