/users?order=post_count&period=monthly implies that it displays all users that made a post in the last month, ordered by post count.
If I scroll down to the end of the list there are users with replies logged for the period, that didn’t actually make any.
Here is an example: (1 reply recorded in the period of Jul 31 - Aug 31, last post actually back in March).
This user has never responded to a PM and has no flags.
Am I misunderstanding the report, or is the data unreliable?