Lucifer, Stay. Good Devil. - S1-E2
Other mistake: We are shown several times the first person perspective of a paparazzi camera, with the HUD. From a diegetic point of view though, it is used in a way that lacks coherence. For instance, in the red carpet scene the photo count goes down by one every time the shutter clicks, while in the car scene it does not go down at all. And it really could not have been Josh's camera in the red carpet scene, because it photographed Chloe once he already escaped and from behind.
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: In the interrogation room with Nick, more than once (for instance when Lucifer says at the beginning "I don't want to know about the case") when Jeremy Davies lifts his open hands and holds them up, they are held up at a different height between one shot and the reverse. (00:18:50)
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: The fake preacher runs away leaving all the money behind: in the overhead shot Lucifer says "I'm here till, well, the end of times actually" turning around past a guy (big hair, big sideburns, black and blue shirt) that he already passed in the shot before as he thanked the crowd. (00:03:20)
Continuity mistake: Lucifer walks down the stairs into 2 Vile's mansion; first person he comes across is carrying a glass, wearing a black T-shirt and grey undershirt sticking out. The guy is walking towards Lucifer as if he were going to use the stairs Lucifer is descending, but just vanishes in the following shot, only to reappear at the next cut, taking the stairs as it seemed bound to happen all along. (00:16:15)
Continuity mistake: When Lucifer talks to the killer in agony in the car wreck, blood streaks change on his face between shots (in particular, he has blood coming from the corner of his moith in the last shot, from the side, but he had none a moment before, in close-ups). (00:09:40)
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: Immediately after the close-up on the poster of Demon Town with Penelope Decker, Lucifer holds the trophy. From behind it's evident that Chloe's healthy arm is down her side, but in the reverse shot she has her arms crossed. (00:17:30)
The Would-Be Prince of Darkness - S1-E3
Continuity mistake: Chloe takes the phone in Lucifer's hand as he is watching the registration. Depending on the angle Chloe has her right hand on the phone itself or off it, signaling Lucifer to stay put. (00:13:15)
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: Talking with her daughter at the end of the episode, Chloe stifles her laughter with her hand in front of her mouth. In the matching reaction shot her hand is still on her chest. It happens again twice. (00:40:30)
Lucifer, Stay. Good Devil. - S1-E2
Continuity mistake: When Chloe asks Jimmy about Lucifer at the end of the episode, her good arm is down her side when seen from behind, or folded in the frontal views. (00:42:25)
Continuity mistake: In the scene in the warehouse, Chloe and Lucifer end up right below where Corazon is tied up. Then blood drips on her hand prompting her to look directly above her head. In the next shot Lucifer turns around and suddenly they're both meters away, looking at the contraption from a distance. (00:26:50)
St. Lucifer - S1-E11
Revealing mistake: When Chloe is getting dressed at the start of the episode, she is wearing a flesh colored bra underneath the bed covers that she has wrapped around her when she mentions her ex dumping her by text.
Visible crew/equipment: When Lucifer jokingly says to Ricky that there's "nowhere to go but up", part of the crew/equipment is reflected in Ricky's glasses. (00:15:00)
Other mistake: When Lucifer and Chloe are talking about the Player after-party, the same extra walks by twice (in the same direction without having enough time to double back). After Lucifer says "sex afterward" and it cuts back to Chloe the women is seen and then when Chloe walks away.
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)
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)
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)
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 ★