Accidentals added to trill lines not displayed until redraw
Add a trill from the lines palette to a note.
Select the trill line and click an accidental in the palette
Result seemingly nothing happens except the score display jumps to the beginning of the score see #309970: Adding accidental to trill line causes display to jump to start of score for this issue
Force a redraw (I usually select a rest and press up arrow followed by down arrow
Result the accidental is now visible