When moving playlists from Rekordbox PL to Traktor PL, key does not transfer. Key Text does, however.
Rekordbox doesn’t have the equivalent to ‘key’ and ‘key text’. It only provide on key value which is the one I use when reading.
Key in Traktor is basically the value calculated by Traktor. This will never be overwritten by Rekord Buddy but you can set Traktor to use ‘key text’ instead which is the value that Rekord Buddy uses when writing to Traktor.