From memory, an initial workaround was included in 2.3 which automatically decreases the number of students displayed per page, based on the number of grade items and your current max_input_vars setting. That caused quite a bit of confusion, though, so a new workaround was included in 2.3.5 and 2.4.2 (MDL-35074) which no longer needs (and therefore removes) the automatic students-per-page limit, putting control of the page size back into the users' hands.
-Paul