Continuity mistake: When Chloe is kicking Lucifer out of the kitchen at the start she has her hands on her hips in one shot and down by her sides in the next. When Lucifer finally admits defeat and says "Fine" (00:04:00)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: As Lucifer is leaving Linda's office, she has hold of her shoe up by her chest. When the shot changes it's now in her lap. (00:40:05)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: Lucifer looks at the file of Ty's ex and isn't holding the file in one shot but is in the subsequent shot. (00:21:00)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: Ty's agent places the folder down for Lucifer and Decker to look at. The position of the folders changes in subsequent shots. (00:20:50)
Continuity mistake: At the beginning of the episode, a cop pulls Lucifer over. The car stops with the front wheels on white road markings. When Lucifer is shown taking off again, the street is just not the same, there's no white horizontal lines, and a manhole appears under the car. (00:02:45)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: Lucifer enters the conference room of the "rebranding" of Ty. You can see Ty turn around in his chair, but after the cut he is still leaning against the table, performing the turn again a second later. (00:35:30)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: At the end of the episode, the therapist in the first part of the conversation (before she gets her heels) holds her right hand on her bosom in the close-ups, while it is lowered in the wider angle. (00:40:10)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: Joe rubs his protege Ty's shoulders saying "But we kept it out of the press." Ty has his hand raised, while in the shot before he had it on the desk. (00:35:15)
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: Lucifer easily walks past the police tape and approaches Chloe and Dan. The same paparazzis appear behind him (mostly past the police car) and behind them, opposite ends of the road. (00:09:00)
Continuity mistake: At the very start of the episode, the strawberry that the woman bites into changes shape several times between shots. (00:01:30)
Continuity mistake: During the kitchen scene in the beginning, the number of pictures on the fridge keep changing in various shots. (00:03:00)
Answer: Boo Normal and Once Upon a Time were going to be part of season 4, then the show got cancelled (before being picked up elsewhere). As such they were added on to the end of season three as "bonus" episodes, hence the continuity being off. But not really a mistake, just a quirk of broadcasting. Boo Normal was originally going to be between the episodes "High School Poppycock" and "Infernal Guinea Pig" in season 3 before being slated for season 4, presumably because aside from the point you've raised, it was fairly flexible, continuity-wise.
Jon Sandys ★