By design, Engineered Flooring is designed NOT to expand and contract. It is 'engineered' (or made) by running 3 or more wood-strips (or planks) at 90 degree angles at EACH layer. By doing this, if the wood wants to expand in direction A, it's prevented from doing so because the layer above (and/or below) it has its grain running in the OPPOSITE direction which is 90 degrees to direction A. SO, whoever informed you that Engineered Flooring is expanding or contracting is 'misinformed'.
(See FloorSearch.com - Engineered Flooring and More) If there are gaps at the butt-end, this is a problem. I would contact the installer for an explanation. With engineered flooring, no gaps should be left except at the perimeter of the room.