Section part names appear and disappear on relayout
1) open section.mscz
2) go to physical bar 16 (bar 9 of second section).
3) top staff, double-click, up-arrow -> long instruments show up + handles for the slur are now not connected to the slur.
4) other random adjustments make them disappear again and yet others make them show up (eg altering the placement of a dynamic).
See discussion + screenshots at: https://musescore.org/en/comment/936707#comment-936707