I found I was missing bots from challenges in months past if I didn't post for a while.  Coincidence?  Maybe.  Perhaps there's some internal setting that says if you don't participate in X number of days, they figure you're not interested?  I don't know.  But it's happened to me too.  Maybe someone in programming knows ...

"If your pictures aren't good enough, you're not close enough."  ...  Robert Capa