High Description
This effect is especially noticeable in busy CMSes with clustering. Clicking for example on "save and close" will be much slower. Also the login is quite a bit slower, but this will actually load the activity plugin.
It looks like the activity plugin is refreshed (and processes events) when it's not displayed when the user clicks on certain places (wf) in the cms.
Another thing to look at to improve the performance could be the report query which seems to be slow (almost a second) when there are a lot of events stored in the repository.