The influence of the random moving NPC's on the route is causing this. You can try re-saving in front of the Daycare man to change their influence. I have found however that certain spreads are a lot harder to hit than others. For me for example the spread on my Monozu is a lot easier to hit than the spread with 4 passed IV's I've found. While I may not be very good a hitting a seed consistently I have tested this so many times I believe it's not just my sloppy synching causing this.