Deliberate mistake: When Mephisto's true form is reflected in the concave side of the spoon, the reflection is right side up. However, reflections in the concave side of spoons appear upside down. This was likely done deliberately by the VFX artists to make this an easier Easter egg for fans to spot.
Mr. October - S1-E2
Deliberate mistake: After Captain Morrow zaps the Xeno and Hermit, he starts to spray a web-like substance over the unconscious Xeno lying on the floor. The webbing covers it, but it wouldn't have gone under where the creature was lying down. Yet moments later he grabs the Xeno by its feet and lifts it to drag it away, and it now shows that it's fully covered with webbing, even on the underside that the spray had no way of reaching. (00:32:40)