You asked if anyone has "any idea."
Here's one idea: this looks like something that departs from what Excel is designed to handle. That is, what you've created appears to belong in an application designed for drawings, maybe specifically architectural drawings. If you anchored some of the lines to different cells -- or if Excel did the anchoring behind the scenes -- then a different instance of Excel, with slightly different defaults, would produce slightly different sizes, orientations, lengths, etc. The variances look as if they'd fit a hypothesis like that. (That's an educated guess, not a certain diagnosis.)