Factual error: Sue's birthday isn't actually on Leap Day as this birthday is her 15th (in season 4 she celebrates her Sweet 16) and Leap Day birthdays are multiples of 4. The closest leap day birthday in this sense would be her 16th.
Continuity mistake: The popcorn Frankie is eating off her shirt moves around from shot to shot.
Continuity mistake: When Mike reveals that he has a cat at The Quarry, the digital clock in Frankie and Mike's bedroom goes from 2:58 to 3:02 in the span of 1 minute. (00:04:00)