The 31/63 issue for me is that they appear to be aligned differently to the 0s directly above them. The left-edge of the 6 seems to be further left than the left edge of the 3. The 3 in 31 at least looks vertically aligned with the 0 above it.

However, I suspect they both have the same ("Incorrect" seems too harsh a word... "Visually imprecise"?) layout constraints and they look different in practice because "63" is a wider number than "31".