MuseScore 3.6 forgets custom chord symbols
Every time I open a score in MuseScore 3.6, the chord symbols from my custom style sheet are replaced by a combination of the chord letter and an unrecognizable symbol wherever a flat, major 7/9 or other symbol should appear. I can restore the custom style sheet symbols by reloading the style sheet (Format > Style... > Chord Symbols), but the score reverts to the jumbled symbols when I close and reopen the file.
Attached image shows a page from a score when first opened (left) and after I have reloaded the style sheet (right).
How do I get 3.6 to remember my custom styles?