Did you test your extension both on light and dark modes of Twitch to ensure your configuration page is legable on both?
I had a denial recently as my config page, whislt containing text, was completely invisible on light mode Twitch. As I forgot to test light mode.
So the tester may have only tested your extension config page under dark mode and you didn’t have any CSS in place to ensure legability. Regardless of the Twitch Theme the user has selected