Cards must be released on a cell — the intersection of a lane and a time box — or on another card to nest. Released anywhere else, the card springs back.
If a card returns to its original place after a moment, the save failed. Shorter Loop deliberately restores the previous state rather than showing you a position that was never stored. You will normally see a message such as “Could not move that item.” Check your connection and try again.Related: How do I move a card?