Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: At the beginning, the preacher is walking around with the donation mug. The first kid to put a few bucks in does it across two shots and has a very notable yellow hand-held device when he puts the money in that was not there in the first shot. (00:02:00)
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: The quantity of blood on the door changes between shots, incoherently, when Jimmy is hurting himself, smashing his head on it. (00:42:35)
Continuity mistake: During the scene in the school corridor with Lucifer sitting down and talking to Chloe's daughter, the same extras keep doing erratic back-and-forth for no reason (for instance the girl with a white jacket and pink shoulder bag) or just plain wrong (the kid with the horizontal striped maroon sweater who walks twice past Lucifer early in the convo). (00:24:50 - 00:25:50)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: Lucifer gets waken up after his very PG foursome by Ty. When he says "Can you just help me, please?" Lucifer does not have his right hand on the shoulder of the girl, in contrast with the earlier and following take. (00:06:15)
Continuity mistake: When Lucifer helps Amenadiel, who has been stabbed with one of Mazikeen's daggers, Lucifer has one hand on Amenadiel and one by the dagger. The camera cuts, and now he has both hands on Amenadiel. (00:21:45)
Continuity mistake: When Linda asks Amenadiel if he is a real doctor, he has both hands raised. Camera cuts and now he only has one raised. (00:08:20)
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)
St. Lucifer - S1-E11
Continuity mistake: The way Malcolm holds the gun when showing it to Dan changes between shots. Note his grip. (00:06:30)
St. Lucifer - S1-E11
Continuity mistake: Just after saying the widow could hold the charity event at Lux, Lucifer has his hands clasped. As the camera changes angle changes however his hands are apart. (00:07:30)
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)
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)
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 ★