I initially thought this was just a function of reading the same thing multiple times, but I’ve since had it happen many times when reading something completely new. Somehow my mind wanders and when I tune back in, not only am I reading clearly, I’m still doing the voicing for different characters. It’s so weird.

I haven't had it happen while reading aloud (since I almost never read aloud), but I've definitely had it happen while reading something new that I hated. I'd end up having to read the same page (or more!) three or four times because I kept zoning out.

By the 3rd week of Goodnight Moon at bedtime, are you still reading the printed words?

No, because the kid has learned to anticipate what's to come, and reading it becomes a game or performance art.

Throw in an occasional Goodnight Opus and learn to depart from the text