Pineapple Fever/Chum Caverns - S6-E23
Continuity mistake: In "Pineapple Fever", Spongebob re-scrambles the jigsaw puzzle right in front of him and Squidward runs outside. In two shots, when Squidward returns, the jigsaw puzzle pieces have moved to the left on the screen, almost behind Spongebob.
Continuity mistake: After going through the curvy air ducts, Mr. Krabs, Spongebob, Squidward and Patrick land in a metal box. In the next shot, Mr. Krabs picks up a Krabby Patty wrapper that wasn't previously there.
Continuity mistake: Patrick smashes a walkie-talkie that Squidward is holding. In a few shots, the smashed pieces that were on the ground have disappeared.
Continuity mistake: Patchy the Pirate wakes up surrounded by other people in the green room. Lincoln lifts up his hat to reveal a Spongebob plush, and Patchy points at it while lying on the floor. In the next shot, his arm is now at his side.
Little Yellow Book/Bumper to Bumper - S9-E4
Continuity mistake: In "Bumper to Bumper", Mrs. Puff gets out of the boat and asks Spongebob to switch seats with her, and Spongebob is wearing his seat belt. In the next shot, once she has made her way around the boat to the side where Spongebob is sitting, he is no longer wearing his seat belt.
Patrick's Coupon/Out of the Picture - S10-E10
Continuity mistake: In "Out of the Picture", when Squidward and Spongebob are running back to the Krusty Krab while being chased by Mr. Krabs, a shot of them entering the establishment shows an empty restaurant, but in two shots, once they've entered the restaurant, the paintings and the art expert are now inside it.
Patrick's Coupon/Out of the Picture - S10-E10
Continuity mistake: In "Patrick's Coupon", when Patrick is kicked out of the ice cream store, he is covered with ice cream. In a close up shot, he has a huge amount of ice cream on him as well as as a cherry. When it cuts to the next shot, this pile of ice cream and cherry have disappeared.
Patrick's Coupon/Out of the Picture - S10-E10
Audio problem: In "Out of the Picture", Larry is holding a fork in his hand when Squidward shows him his painting. In the next shot, Larry raises his claw and the fork is no where to be seen and no sound of it clattering is heard.
The Fish Bowl/Married to Money - S9-E18
Continuity mistake: In "The Fish Bowl", Sandy has a wristwatch on her right wrist when she first appears on the bus. When she sits near the front to observe the fish, the wristwatch has disappeared and doesn't reappear.
The Fish Bowl/Married to Money - S9-E18
Audio problem: In "The Fish Bowl", after Patrick takes the bowls of ice cream and eats them both, he throws them behind him. The bowls just disappear in mid air without leaving the frame (also an "other mistake") but the sound of the ceramic bowls breaking is still heard.
The Fish Bowl/Married to Money - S9-E18
Continuity mistake: In "Married to Money", Pearl cries and her tears flood Mr. Krabs' house. When this happens, he pulls a in the floor to let the water drain. In a few shots, this plug and drain are missing.
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.
Krabby Land / The Camping Episode - S3-E19
Other mistake: In "Krabby Land", Mr. Krabs as "Krabby The Clown" finishes his short speech and goes into his office. When he slams the door, bubbles float up and those bubbles stay motionless in the air for a few frames.
Krabby Land / The Camping Episode - S3-E19
Continuity mistake: In "The Camping Episode", Squidward sets down a blanket to lay under the stars and in a couple of shots, the blanket disappears.
Krabby Land / The Camping Episode - S3-E19
Continuity mistake: In "Krabby Land", Spongebob goes to check his motivational quote and from far away, the page is flipped up. But in the next shot, it is a close up and the page is flat against the stack. In the following shot, the page is flipped up again.
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.
Jellyfishing / Plankton! - S1-E3
Continuity mistake: In "Jellyfishing", Patrick and Spongebob slide down two ropes and burn their hands on them. The two shots after they land show them trying to cool down their hands and in the shot after that, the ropes they had just slid down on have disappeared.
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.
Born Again Krabs (aka A Penny Saved) / Safety Freak (aka I Had An Accident) - S3-E17
Continuity mistake: In "I Had An Accident", Sandy opens the door to show that she was being "attacked" by a gorilla and Spongebob is looking through that door to see the events unfold. But after a couple of shots, the door has closed by itself and Spongebob has to open it again before going outside.
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.
Answer: I believe this is the Season 6 episode "Spongicus".