How I understand is that they had printf(x) somewhere and some values of x included the '%' character. If this has been inside the UE and the x itself was a has

How I understand is that they had printf(x) somewhere and some values of x included the '%' character. If this has been inside the UE and the x itself was a hash value then both replacing with printf("%s",x) and changing the x's value could be problematic.