Every night, the stored procedure sp_checkClientState is supposed to run, which is supposed to check each client's date of last activity and update their activity/inactivity status accordingly. It appears that this procedure is not always being called when it is supposed to, which is resulting in a number of issues related to activity/inactivity.
See also:
Clients are going over the inactivity threshold but not becoming inactive (60.3)
RecentActivityDateTime is null
Stored procedure sp_CheckClientState not being initiated