Why does my profile pic keep changing?

When I look at the leaderboard sometimes it’s my old pic, and sometimes it’s a generic avatar. I’ve been various things recently, a white girl with dark hair , a black boy, and just now I had someone else’s actual photo!?! If I click on the avatar to go onto my profile page, there’s a blank space where I haven’t picked an avatar since the change. Which may be the problem. When I go back and look at the leaderboard again after doing this, my old profile pic has returned. I’m not overly bothered, but it was rather odd to see someone else’s actual photo there 😆 anyone else had this?