That's the"skip mode", it skips text that you've read already (in case you go back to a chapter or reload an old save for some reason). You can change this to allow it to skip any text in the options menu (along with an option to make it stop skipping during decision moments or not).

There's also probably a different button (never played with a gamepad) for "hard skip", where you skip any text, read or not, as long as the button is held down.

ah thanks