How timely! Bella has started doing the same thing pretty much. She is normally a vacuum, but the past few days she's been stopping mid-meal...sometimes going back to finish, sometimes not. She also eats much slower than usual. She eats Fromm puppy, as well.
Since your pup is 8 months, I think you can start adult food. Once my Fromm puppy is gone (another month or so), I'm going to adult formula. Bella is 5 months old today.