I have a drawing with dimensions etc, but a couple are missing one extension line, even after re-opening drawing & re-dimensioning (if that's a word).

Please see attachment to see what i mean.

is this a software error, or something to do with the graphics card?

Asus Laptop, Win8.1 Pro, SW 2016.

i7-3630QM CPU @ 2.40GHz

Intel HD Graphics 4000

nVidia Geforce GT 635M