This issue intermittently pops up. Most of the time using automatic allocation successfully allocates large numbers of submissions for peer reviews exactly as expected.
We are using scheduled allocation, together with automatic switching to the next phase after the submissions deadline.
It has happened four times on separate occasions that students were allocated 4-6 submissions instead of the 3 as per settings.
All settings are correct as per MOODLE docs.
Our students are spread over the world and live in different time zones. By the time we notice the allocations are wrong, some students have already started their reviews. Re-allocating, when some reviewing has already been done, causes even more submissions to be allocated on top of the ones already allocated (even if you select reset/ Remove current allocations).
We have also noticed strange logs that looks like students switched the phases. From our understanding the bizarre allocation problem is triggered when a student access the workshop activity within milliseconds of the phases being switched over.
This relates to https://tracker.moodle.org/browse/MDL-51262