I have realized that if a song title or an interpret name includes special characters like „ä ö ü ß“ etc. this songs won’t show up in crates / playlists if you open the Serato library in Engine Prime. Funny wise the same playlist used in iTunes (opened in Engine Prime) will show up correct.
For US / UK no problem - but I am form Germany in this region of the world this characters are used quit often
As already commented in another post in my case crates will show up anyway only if prepared without any substructure - which means totally flat (all on level 1) - which is a nightmare btw.
Im using a MAC 10.11.6 El Capitan