Hidden blue line?
The green line going up and left, is there a blue line almost completely hidden behind it? Maybe my eyes are just tired...
Are you referring to Slice view? It looks like a blue (teal/aquamarine) line does run along approximately the same path as a green line. The 5-10 and 10+ options come in handy in this situation when marking an off-center vertex. It's perfectly fine if you're not able to annotate the exact number of lines, so long as it's close!