Challenge owns dropping

Is it normal that number of completed challenges drops? When machines are retired number of “owned” machines does not change, just the points. But with challenges I found that I have fewer "owned’ challenges. It never happened to me before.

Yeah man I think that’s normal like there’s gonna be new challenges and old challenges are retired and they don’t count anymore so you got like “totally owned challenges” out of all existsing like that’s not gonna count cause they’re retired, you know?