I'm assuming you mean what you see visually and what you hear don't match perfectly.
That doesn't
necessarily
indicate the actor isn't singing. It's common, even when the actor is doing the singing, to record a song in a regular recording studio and have the actor lip-sync to his own performance.
Then again, there's no particularly compelling reason
not
to use a better singer to do the singing and a better actor to do the acting.

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If you listen to Paul singing, its a little off.

They may have, as the man who played John Lennon was a singer in a band!
"The face of evil is ugly to look upon. And as the pleasures increase, the face becomes uglier."

Definitely not !!