Issues around last_visited_at also reported / detailed here:
Specifically on April 7th I concluded the table is not updated correctly.
I’m unsure if there have been any code updates in this area since.
I didn’t report it in the #bug category because there is nowhere in Discourse code base where this was an actual “problem”…
… however data is stored in an inconsistent manor for other plugins and custom users reports to be ran against.