First of all, I would really like you to remove the next/previous links in the activity log. Make it all on one page, PLEASE! At least allow us to select how many items per page with the option to choose "all"
That said, there is a bug with the next/previous filter.
If you filter with a start date/end date with a student that has more than 10, then click the next button everything works fine up to this point. The problem is if you now change the date it appears to maintain the "next" state occasionally displaying no results at all.
If I change one of the other filters such as "activity type" from all to exercises then back to all it seems to reset the next/previous states.