Or it could possibly be that one chapter was less exciting than the rest and other series simply outpreformed it this time. At this time it's definitely not a downfall and I wouldn't worry about it until it gets 4 bottom 5's in a row, which is highly unlikely at this point. I wouldn't jump to your conclusion from 2 reasons :
1)What series that is above it need the reprieve? they're already established
2)Why not do it with a more stable series, or any other series such as Soma or HQ!!?
It was stated in Bakuman, most readers have a brain and don't just follow their series like zombies, if they liked something more(or 3 somethings for that matter)in the specific week, they will vote for for it. Just look at other bouncing series and see.