Both happens. When an appellee becomes inactive and when a staff becomes inactive/(or probably something else). No idea which occurs more often though.
Like this one
The appellee became inactive.
And sometimes like this one. Both sides are active, appellee and the assigned staff but the content of the appeal isn’t correct… then… it just gets ignored until it gets corrected or bumped by the appellee. But this one got ignored in the end . Wierd ban a few years ago - #4 by VoidFox2008
There are other reasons why it closes, but yeah(?) more on the staff side.
Oh, I’m just showing examples here.