Incomplete means that those pathlines ran out of "steps" to reach the outlet. Typically it means that they went into a reciculation zone and didn't leave, but in this case the large number could just mean you need to increase the number of steps. 5000-10000 maximum steps in a steady case is sensible, above that and you tend to use up cpu for no real benefit as the pathines are just orbiting a point somewhere.
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