There is a Lost example of a trap door that really wasn’t, as like Babylon 5’s later seasons, the crew in Hawaii had to deal with approaching an end game that didn’t require everyone’s involvement. That’s why they brutally killed Elizabeth Mitchell’s Juliet using a deep, dark hole and a hydrogen bomb, but this led to fans immediately speculating that she died because Mitchell was starring in the new series V. For years, this was accepted knowledge among fans, but the timing was actually backward, and Mitchell got the offer for V because Juliet was going to die, and the network wanted to keep her around.
So while this wasn’t actually a trap door, Lost’s lack of planning is still felt here compared to the intricate narrative of Babylon 5, as Elizabeth Mitchell has said in interviews that the producers had no idea what to do with Juliet at first, and left her past as a mystery not to be sneaky, but because they had no idea what it was.