Other mistake: When Maze is knocked down by Lucifer the second time, the footage used of her on the ground is the same footage from when she got knocked down the first time.
A Chance At a Happy Ending - S5-E16
Other mistake: After Amenadiel's necklace pin is removed, Chloe tells lucifer to get the blade, and he picks it up with the hilt still attached. But we saw in an earlier season that without that pin to hold it all together, the hilt just falls off.
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 ★