During the flashback murder scene you can see that Morticia has long black fingernails when she picks up the sword to stab Garrett at 32:43 but at 33:30 her nails are gone for the remainder of the scene.
At 43:53, a group of three individuals is seen walking past in the background. At 44:17 the same group is seen again walking past, in the same direction.
The show quotes "Fire will rain" in Crackstone's crypt as well as a message burned into the lawn. Then when the characters are inside the Gates mansion the altar reads "Blood will rain." Whether the error is on the altar or in the message burned on the yard, Laurel Gates would have not made that mistake.
When fighting, Garrett Gates is far away from the edge, and well inside the columns. Without stepping backwards, the next second, he is right at the edge, about 6 feet further back, and beyond the columns.
Wednesday's ancestor, Goody Addams, is treated as though "Goody" is her first name. The term "Goody" was a term used in olden to address women, short for "Goodwife," in the way that "Mrs." is used in modern day. It was not a name but a social title.
Wednesday says that she can determine that Gomez is lying because she recognizes his "tells" from when they played Russian roulette. Tells are an indicator that someone is being purposefully deceitful, such as in a game of poker when one wishes to hide the strength or weakness of their cards. As the results of Russian roulette are completely up to random chance, there is no opportunity to try to lie to your opponent.
When the session with Dr Kinbott is over, the cuckoo clock goes cuckoo twice, even though the clock hands show it is one o'clock.
The sword blade that Gomez stabs Garrett with changes length between shots.
In flashbacks to 32 years prior, Gomez is much taller than Morticia. In the present day of the story, Gomez is now visibly shorter. He would have had to have shrunk and she grown at a time in life when most people have already reached their full height.
A second generation Ford Explorer is shown in the 1990 flashback even though it was produced from November 1994 to December 2000 for the 1995-2001 model years.