Why do friends disappear from recent activity?

[user-removed]

My Question or Issue

I follow my daughter on Spotify and she follows me too. But sometimes she is not visible at all on my friends Recent Activity.

in what situation would a followed friend disappear from Recent Activity? If they are in private mode, do they disappear or continue to show only the last public song played? If they log out of Spotify do they disappear from Recent Activity? Also, after a certain amount of inactive days do they disappear?

[generaldrillham]

I'm actually very curious about this as well. I haven't seen any information on specifics here.