It seems I saw a note on their home page a couple of weeks ago that said that they were trying to process payments more quickly in December and that some payments would arrive early. Payments were to be issued based on the time the work was approved by Intelli-shop as opposed to when the work is done, so I would guess that they approved the shop for which you've received pay already just before their internal deadline, but did not approve the others until a day or two later - even though you did the other shops first.
I received payment today for a shop I did 12/10. However, I have not received payment for the shops I did 12/17. I am anticipating payment for those shops to arrive around 1/20.
Hard work builds character and homework is good for your soul.