Column "Last visit" in course member management doesn't show correct lastModified value

In the course member management, the column "Last visit" is supposed to show the date and time of the last visit to the course. However, the column shows some other "lastModified" value. Changing the membership of a member sometimes changes the date too, but not always.
Even as admin, the date of my last visit to a course (https://testing.frentix.com/test8/auth/RepositoryEntry/292192256/MembersMgmt/0/Members/0) isn't up-to-date.