Comment 2 for bug 786791

The easiest solution is to just change Y coordinate to an integer (for instance, your blurry line is at 855.750, changing it to 855.0 solves this). The extension pixelsnap serves this purpose (Extensions->Modify path->Pixelsnap).

The underlying "problem" is that it is impossible for any software to fit a 0.5 line in a pixel grid. At some point the software has to cheat, either anti-aliasing the path or just turning them (for screen output only) into 1px lines.

It seems to me that at 100% zoom Inkscape turns the 0.5 px line into a 1px line, at least for the non blurry line.

The fact that some lines are blurry while others are not is beyond me. Definitely it depends on the Y coordinate, but I guess that internally Inkscape processes them differently depending on their position.