The first time Clayton Boone drinks iced tea with James Whale, Clayton drinks most of his glass at once. The next time we see Clayton, his glass is almost full again.
When Clay is in the diner and is about to watch La novia de Frankenstein (1935) on TV, Harry is reading a paperback book but in the next shot, he is reading a pamphlet. And when Clay says, "We're watching the damn movie, Harry," Harry is holding a book again.
When Whale is playing "strip interview" his cigar case appears and disappears from his hands between shots. He also opens it twice.
When talking about Whale wanting "to draw him like a statue" Clayton tosses away his towel twice.
When Hanna stands up to turn the TV off, she throws her napkin/towel on the small table in front of her. It covers most of the table, and also part of her plate (on the right side of the table). When she has turned the TV off and looks back at James, we see the towel lying neatly on the left side of the table.
In an early flashback to James Whale's childhood in England he is accused of "lollygagging" - an Americanism that is not known or used in Britain.
This movie falsely says that Boris Karloff wasn't in any movie prior to Frankenstein. This is false! He was in SEVERAL films BEFORE Frankenstein. More notably the criminal code 1930 and graft 1931.
The Eagle Globe and Anchor on Clay's lighter at the top of the movie is backwards.
The Autumn Harvest Pyrex bowls seen in the movie were designed by Richard Hora and manufactured only from 1979 until 1986.
The Fiesta disc pitcher used by Hanna in the studio is the post-1986 yellow not the original yellow that would have existed in 1957.
In the interview with Kay at the start of the movie, Whale claims to have been born in London. James Whale was actually born in Dudley, Worcestershire (100+ miles from London)