Notes using lettered note heads do not render well in mobile apps.
Consider the following file attached. It uses named noteheads which render well on Mac, PC and upon upload, Musescore.org.
If I check this same score in the mobile app (iOS in this instance). Some of the noteheads are missing. The note itself is there and plays fine in playback but it is visually missing the note.
If I turn off notehead letters and reupload the notes render as expected.
This only seems to impact the mobile app. Which notes are impacted seems to vary, it is not the same notes each time.