Quoted from isJ:Seems to only happen in the right lane and it's not always based on kicking out of the VUK. Maybe it thinks it's being booted from the shark hole..
If the ball drains out the right with enough speed, it will go past the drain and into the subway scoop on the left. From there, the game will kick it into the trough but, since it didn’t register a drain, it will give the ball back.