Nature Pants / Opposite Day - S1-E9
Continuity mistake: Opposite Day: The front door knob on Squidward's house repeatedly switches between the left and right side of the door, so it opens the opposite way (it has nothing to do with it being opposite day).
Mermaid Man and Barnacle Boy / Pickles - S1-E6
Continuity mistake: Mermaid Man and Barnacle Boy: Mermaid Man wears green tights, but after SpongeBob absorbs the water ball like "some kind of evil sponge," when Mermaid Man and Barnacle Boy start doing the dog paddle, Mermaid Man's tights have vanished in this shot.
Mermaid Man and Barnacle Boy / Pickles - S1-E6
Continuity mistake: Mermaid Man and Barnacle Boy: When Barnacle Boy opens the box with the two rings inside, in the closeup the "B" ring is on the left and the "M" ring on the right, but in the wideshot Barnacle Boy removes the ring on the left (the "B") and places it on Mermaid Man's finger, then in the next shot we see it's the "M" ring, before both rings vanish.
Mermaid Man and Barnacle Boy / Pickles - S1-E6
Continuity mistake: Mermaid Man and Barnacle Boy: When SpongeBob and Patrick (dressed in their superhero costumes) exit the pineapple the front door opens at the right side (outward), but after getting on Squidward's nerves, when they retreat back inside the front door opens the opposite way at the left side (inward).
Scaredy Pants / I Was a Teen-age Gary - S1-E13
Continuity mistake: Spongebob's belt is missing when his clothes are first revealed while dangling in midair.
Scaredy Pants / I Was a Teen-age Gary - S1-E13
Continuity mistake: The Krusty Krab is filled with Halloween decorations during the episode, but when Spongebob jumps to hide in a barrel there are no decorations in sight.
Scaredy Pants / I Was a Teen-age Gary - S1-E13
Continuity mistake: When Spongebob agrees to hear Mr. Krabs' story, their seats come out of nowhere.
Hooky / Mermaid Man and Barnacle Boy II - S1-E20
Continuity mistake: In "Hooky", Spongebob is being pulled by the hook and grabs onto a flower to try and hold onto it and it becomes limp. In the next shot, this limp flower he just grabbed has vanished.
Pizza Delivery / Home Sweet Pineapple - S1-E5
Continuity mistake: In "Home Sweet Pineapple", Spongebob goes into Squidward's house to spend the night and sits in his bed with the pillow just the right size for him. But in the next shot, when Squidward climbs into bed next to him, the pillow has drastically grown and now both of them can lay on it perfectly.
Pizza Delivery / Home Sweet Pineapple - S1-E5
Continuity mistake: In "Pizza Delivery", Spongebob points out the antennae for the boat during his vehicle inspection, but in a few shots, when he's checking the tire pressure, the antennae has vanished.
SB-129 / Karate Choppers - S1-E14
Continuity mistake: In "SB-129", every time Squidward goes to answer the door to find Spongebob and Patrick there, the picture on the wall next to the door changes noticeably.
Bubblestand / Ripped Pants - S1-E1
Revealing mistake: In "Ripped Pants", Spongebob plays the guitar and chord changes are heard, but his fingers on the neck of the guitar do not move.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In "Opposite Day", Spongebob pushes Squidward through the sand, leaving a pile of sand. Two shots later, they are now on Spongebob's sidewalk and the sand pile has disappeared.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In most of the show, Squidward's house only has windows on the front of his house. But, in "Opposite Day", he has windows on the "ears" of his house, which don't appear throughout the show.
Nature Pants / Opposite Day - S1-E9
Continuity mistake: In "Nature Pants", Spongebob comes back home, where his friends have thrown a "Welcome Back" party for him. When he enters, two balloons float behind him. In the next shot, they disappear.
Bubblestand / Ripped Pants - S1-E1
Continuity mistake: In "Ripped Pants", we see 3 other people at the square lifting weights besides Sandy. When Sandy lifts her weights, the crowd cheers, and we get a wide shot of the square, we see that the 3 thugs are gone.
Help Wanted / Reef Blowers / Tea at the Treedome - S1-E2
Continuity mistake: When we first see a far shot of Squidward's house, there is no potted plant on his porch. When Squidward steps out, the potted plant appears, and he rights the crooked flower. The potted plant disappears in the rest of the shots of Squidward's house.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "F.U.N.", Plankton uses a laser to get through the secured Krusty Krab. When he does this, we can see the outside. In the next shot, the hole is now gone.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "Culture Shock", Mr. Krabs arrives in a wheelbarrow of money, with several bills landing on the floor. In a few shots, the money has disappeared.
Culture Shock / F.U.N. - S1-E10
Continuity mistake: In "Culture Shock", Squidward is waiting next to a slightly opened curtain. In the next shot, the curtain is completely closed.
Chosen answer: You need to provide a little bit more information to be able to answer a question like this. In what region is it not being shown? I see it being replayed here in Australia fairly frequently. As for a general reason, there does not appear to be any for why it specifically might have been taken off the air in any country or region. Like any show certain episodes can sometimes not be replayed for long periods for unknown reasons.
Lummie ★