Another MT might have that particular doctor as a higher priority in their pool. For example, I have a doctor that used to be exclusively mine. They eliminated exclusives, but my TSM still has that doc come up as 1st priority for me above all other docs on that same account. Others do have access to him too now, but he comes up as a 1st priority for me but not for the other MTs. Even if there are reports from 9am in the pool, and my old exclusive doc uploads at noon, he will shoot to the top for me.
It could also be that a particular MT has been taken off certain docs on an account and only has access to a few "easier" docs.
There are actually quite a few reasons you could be seeing reports disappear from the middle of your pool. You have to keep in mind though, the middle of your pool might just be the top of someone else's pool. It all depends on how that particular pool is set up.