UPDATE! Solved (but don’t know how)
I’ve been on a trip for a week. During the trip I didn’t have access my raspberry pis through the Spotify connect in the native spotify iphone app as described above. When I got home yesterday evening I updated squeeze server again (just to be make sure I had the latest version if there was any update when I was away) and rebooted the system and…voilá…now everything works as it should again. The spotify connect appears in the native spotify app in my iphone and can control Spotify even when I am not on my home network. I have no clue why it started to work again but am happy that it does. Maybe it was the update procedure I carried out late last night. Anyway, thanks for looking into the issue and thanks for the amazing Max2Play.