For an Alto Sax Instrument, I added the standard accidental Flat U+E260 (and 266D) into a textfield (by copying/pasting from smufl) during writing.
Although the name is displayed correctly on the wrting menu, the graphical character is omitted when shown on the print menu, and not printed as well.
Make sure you explicitly set the character style for the flat character by selecting it in the text editor and setting the character style to ‘Music text’.
Working, thx.