
Liar, Liar, Slutty Dress on Fire - S2-E2
Continuity mistake: When Lucifer gets the doll out of the box, the doll's box is either face up or face down depending on the shot. (00:24:30)

Liar, Liar, Slutty Dress on Fire - S2-E2
Continuity mistake: When Lucifer is examining the doll, the way he holds it changes between shots. In one shot, he is holding the packaging, and in others, he's holding the item. (00:24:20)

Everything's Coming Up Lucifer - S2-E1
Continuity mistake: When Chloe goes to ask Ella if she believes in God, Ella has her hands on or off the microscope depending on the shot. (00:32:20)

Everything's Coming Up Lucifer - S2-E1
Continuity mistake: When Lucifer walks out of the police station having worked out who Bobby B is, Chloe has nothing in her hands in one shot, and a piece of paper in the next. (00:30:40)

Everything's Coming Up Lucifer - S2-E1
Continuity mistake: When Lucifer and Ella are talking for the first time, Ella's hair changes from neat to messy between shots and back again. (00:08:50)

Continuity mistake: When Chloe turns the picture of the cufflink upside down to Dan, her grip on the photo changes between shots. In one, she has one finger behind the picture, but in the front angle, all of them are at the front. (00:33:10)

Continuity mistake: When Onyx opens the box, the way he holds the lid changes between shots. (00:19:50)

Continuity mistake: At the start, the man's hands change position around the woman during instant cuts. (00:01:40)

Continuity mistake: When Lucifer is walking towards the cowering Lindsay, she has her gun in her left hand. When the shot changes to behind Lucifer, the gun is now gone. (00:34:20)

Continuity mistake: When Lucifer hands Linda the leaflet in the carpark, the way he holds it changes between angles. In one shot he's holding the sides and in the next he's holding the top. (00:25:40)

A Priest Walks Into a Bar - S1-E9
Continuity mistake: When Malcolm asks Amenadiel if food tasted this good before he died, his hands are clenched into fists with one finger pointing at the food. When the shot changes his hands are open and just facing forward. (00:39:20)

Favorite Son - S1-E6
Continuity mistake: When Dan confronts Mazikeen over leaving him in Chloe's apartment, he has his arms outstretched in the front shot and down by his side in the reverse shot. (00:21:20)

Sweet Kicks - S1-E5
Continuity mistake: The position of the guys Mazikeen attacks changes between shots. Note the woman Chloe knocks out. (00:31:30)

Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: When Lucifer shows his devil face to the preacher at the start, the mascot behind Lucifer changes between 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 ★