In NESmaker, when you import music... it will add a mbunch of musics and sfx. But then, you can't remove them.
So, if you're ok with the tutorial music, go for it. If the music become annoying... you will not be able to remove it
The only way to change music is to re-import a music famitracker txt file (to replace the current musics in your project).
So, if you want to import music, just to test if it's related to your flag issue... I'd suggest, first, to just comment out the line in the code.
If the issue remains, it means it's not related to the missing music.