I am not really sure what is the reason behind this scenario since the other phrases I am working with the root keyword "residual income" are all doing well. They are all now in the first page of Google and they are now receiving clicks although the click-through rate is still not that high.
But I am now concentrating on "residual income online" since this is the keyword that received the highest number of clicks among the other keywords. More back links are now made online and I hope this can catch up with the other residual income phrases in due course.