I didn’t find a solution to this problem here, so, although other users are describing this behaviour:
When attaching a file to an Update on Activity Stream this file es is added to Media, but not shown in my Activity Stream, Update text only. My BuddyPress settings are:
Enable media in profile ON Enable media in group ON Allow upload from activity stream ON Number of media items to show in activity stream 0
When attaching a file to in Profile Media, it’ll show up in Activity Stream, as expected.