Tilia,
Is there any chance that the tracks are frozen? Although this should not matter.
When you change the number of choruses to 1 you should answer yes to the question if the song had a melody line, and also save the song before exiting.
Are those steps being taken OK?
(Always a new song will default to 3, but re-opening an existing song should open with the number of choruses that the song was last saved with)

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