[SportsJunky]

The locking system on laminate planks is usually very strong when you initially lock it to another plank but each time you take it apart and re-attach, the lock becomes a little bit less effective. I mention this because you stated that you've already pulled them up once before and re-used the ones that looked undamaged.

Also, a floating floor that is not allowed to float unimpeded usually results in gaps on the short ends. Is the floor tight to the walls? Usually a floating floor needs to have a control joint with transition in all/most doorways but you seem to have that covered. Is it possibly running up against the jambs? Also it appears that the floor wasn't laid on a right angle to the room? Not that this would contribute to the planks separating but it just seemed odd.

The answer may be living with it or pulling it up and re-clicking them together again. Humidity levels might be a contributing factor but that doesn't show up in man made products as often because they are constructed to be much more stable than a natural wood product. Now that I re-read the problem, I see that you mention that the planks come back together in spring/summer so maybe it is more of a dryness issue in the winter time?