I just see that there is now (don't really know whenit arrived) in PoodLL filter plugin a section named "PoodLL support information". I understand the use of this, to help manage problems and have them resolved sooner.
In these information, there is the "number of active users". The problem is that, to obtain this number, there is (i suppose) a calculation made from the log table, and this calculation can be very very long. Moreover, it generates a very big load on the server. On my plateforms, it has taken up to 5 minutes for the biggest one
When, has an admin, you open a setting or information page, you expect to have it open (nearly) instantly, and not to have to wait several minutes.
I really think that this calculation should not be made when you open this page, but on (specific) demand, with a big warning, or by cron, at a moment where the server is less used.