Violins section becomes muddy and out-of-time when two lines are notated on a single staff

Notate a violin section part with double-stops (multiple notes at the same time on a single staff)
Optionally, add a piano for comparison--this makes the muddiness stand out
Play it back--section with double-stops will be muddy, quieter, and out-of-time

Note that this does not happen with a single line, or with two staves of violins playing different lines--see the attached score.