I think they retconned his scar.
Kuai Liang originally got the scar at some point between MK2 and MK3, but that didn't happen in the new timeline. Originally people said that the scar was the "mark of death" that Lin Kuei put on Kuai when he escaped with Smoke, but later MKSM showed that he got the scar from Kung Lao. Neither of those scenarios happened in the new timeline as Kuai was captured by the Lin Kuei before the invasion, and Kung and Kuai never fought in MK9 at all.
This new Sub with a scar might not be Kuai Liang, but then again he could be. I'm leaning towards him being Kuai, but the masked sub...IDK. Boon alluded to this being a new Sub altogether, but then again I believe their is evidence to make a case for it being Bi Han.
At the same time though, that could / might just be another skin (1 of many) for Subzero.