It's the first time that I've already completely finished with a song, but then still rework the song. Although it happened in the last song that I improved the vocal melody at the very end, that was just a detail, while this time I changed the entire harmony of the second part.
The reason for this was that I felt some kind of disruption in the transition from the first part to the second. When I then decided to analyze the reason for this, I realized that the two parts were in a very similar scale, but differed in one note by a semitone. I've often had songs with two parts in different scales in the past, but these scales were then so different that it was obvious when listening. The subtle difference on the current song, on the other hand, seemed like a mistake had happened, and the one semitone seemed more like the note was mistyped, like a different scale. I tried to convince myself that this different semitone was good and innovative, but then I had to admit that I had to change something.
The simple solution of just correcting the second scale by just moving that one semitone to match the first scale did not work because it ruined the song. So I had to reset the harmonies and therefore redesign everything - including the vocal line.
Eventually I succeeded, and the song is better than ever, especially the vocal melody has benefited from the change. Due to the change, the second part has a more melancholic mood than before.