Vanishing Percussion Instruments

In this file I have 2 multiplayer percussion. But in Flow 1 I only see 2 of the instruments… Flow 1 was an xml import. Any advice? Thanks!
test.dorico.zip (708 KB)

Players in flows imported from MusicXML files behave differently from players that you create normally: they don’t automatically gain new instruments as they are subsequently added to the player. (This was an intentional choice but it’s something we discuss occasionally and probably on balance think we should change in future.)

Your best bet is to recreate your two percussion players and add all of the required instruments, then copy and paste the material from the existing players to the new ones.