I agree with you that Newcastle United is not stable this season unlike the way they were last season, this is because they are playing in the Uefa Champions League, and they are not used to such a situation. I think if they don't qualify for the last 16 of the Uefa Champions League they will be consistent in winning matches in the Premier League. Liverpool might be able to get a point from Manchester City at Etihad Stadium because Manchester City is not at their best form this season.
Yes Newcastle are not used to playing in the Champions League, and by playing in the Chmpions League, their schedule becomes much busier than usual. But it was good for them as a very valuable experience, because Necastle is currently a team that has the potential to return to the Champions League next season.
Their focus is divided, and in the Champions League itself I am very sure they will try their best to get a good experience as well. Even though they are now at the bottom of the standings, their chances are still open to qualify for the last 16 of the Champions League.