Go to your game you might have dropped it on different square. There are no such rules on chesscom.
Two Moves
If you want to make sure you don't accidentally drop the piece on a legal-move square (instead of the original square) then move your cursor off the board before dropping it.
Does Chess.com apply strict rules as to "once you touch a piece, that's the piece you have to move?" I did that tonight - picked up a piece, was going to move it, opted not to and dropped it back where it had been, and I lost the turn, and my opponent got to move, which resulted in my opponent winning. That's kind of messed up.