The Shoes: Near the opening, Kramer walks into Jerry's apartment to tell him that he saw Gail Cunningham, when he enters, he leaves the door opens. The scene then cuts to a shot of Jerry and George on the couch, then back to a wide shot of the apartment. The door is now closed. Maybe a poltergeist
The Soul Mate: When Jerry has Newman backed up against the door, the door to right of Newman is 5F, the door to the left of Jerry is 4E. Probrably not a blooper but I'll put it down anyway.
Any others? I'm sure there is.