Sara's hair at the party where Dahrk turns up goes from slightly curly/wavy to very curly then back to slightly curly/wavy. This is most noticeable before and after she and Zari confront Helen.
Dr. Martin Stein, now wearing Jax body after the switch, says that Hedy Lamarr was his childhood crush. The Legends time line puts Dr Martin Stein as being born in March 16, 1950, so he had to be some 10 years to view and enjoy movies and understand beauty and women, so he is talking about 1960. Hedy Lammar was born on November 9, 1914, so must have been about 42 years in 1960, past her prime and having done all her cult movies much earlier than that. Even her biggest hit, Samson and Delilah was a 1949 film, that was before Stein was even born. Thus, the time line is not matching to make Hedy Lammar as childhood crush of Martin Stein, unless the Stein was in to older women.
At the K&G party, Nate mispronounces Cecil B. DeMille's name; it's "Sess-ill", not "See-sill".
After they switch bodies, Jax as Stein says his hands are white, referring to his body's race. Stein as Jax then says his are African-American, and is corrected by Jax that he can just say black. In fact, black is the correct term for race of the character, as Franz Drameh was born in England. Since he is the same race as the black American he is playing, his race cannot be African-American.