Goofs

The food on Emmett's fork disappears.

When he arrives at the train station with Ellie, Emmet stops the car just in time to avoid slamming into a utility pole. When they get out of the car a second later, the pole is not there any more.

During the Hollywood sequence, Emmet's band is backing a black vocalist. In the 1930s, musicians on film were, with extremely rare exceptions (e.g., Benny Goodman's quartet), strictly segregated. There's no way a white band would be playing behind a black woman.

The guitar that Emmett destroys at the end of the movie is (thankfully) not a genuine Selmer Maccaferri. The shattered fragments clearly show a bolt-on neck. The genuine instruments used a bolt during construction, but this bolt was removed before the guitar was completed, leaving an empty hole. (The instrument actually destroyed was a disposable prop created by Michael Dunn.)

Railroad freight cars have reporting marks for railroads that did not exist in '30's

The steel grain bins seen on a car trip would not be found in that time era.

Blanche and Bill drive past a modern Yield sign.

Emmett's guitar playing is completely mis-matched with what is heard on the soundtrack. He plays the wrong chords, doesn't position his hands properly for the chords he does play, and is often strumming when he should be plucking (and vice versa).