eleven reader volume issues

I am using the most up to date eleven reader on my iPhone 13 Pro. when i commence playing an article on the eleven reader app, at around 3 minutes, the volume starts to decrease till it is only just listenable. it stays there for many minutes and will sometimes just jerk back to normal volume. I have reloaded the App, attempted adjusting volume on the phone and more. one final thing is that I like the Brian voice. i have removed two other voices off the Eleven Reader to accommodate Brian. but he will not load. any clues on either of these issues?