RMS Mix isn't listing all of the Parts from my RMS Coach export?
Due to the limitations of mobile, RMS Mix exports via RMS Coach are limited to 16 parts per song.
When you export from RMS Coach, the first 15 listed Parts (i.e. Maria, Gretyl, Nuns...) will get their own, soloable, tracks in RMS Mix. Everything after the 15th part will be summed (combined) to the 16th track in RMS Mix.
Before moving forward, note, that everyone in your cast can download RMS Coach to their Windows or Mac computer and unlock it - thus, giving them access to their parts for solo purposes via computer. But, there are also ways you can make certain everyone in your cast can hear their part solo'd in the RMS Mix App.
One way is to first make a default export of the show with the as-is part order, and then make a second export after editing the part order. In Edit Mode, you can drag the parts up or down in the list to give priority to different Parts in your export.
You could also duplicate any of the songs that feature over 16 parts and then have 1 single exported show that has 2 versions of these special songs (one with As-Is order, another with reordered parts). You can even rename these special songs in Coach so that it's easier to differentiate them later - do this by double clicking the song name while in Edit Mode.