I've got a four year old Trex deck with no such problem. I guess it's something I'll have to look forward to.
You shouldn't let debris accumulate in the gaps. Trex may not need staining or sealing maintenance but I personally think you should give it regular clean-up maintenance. Maybe the debris held moisture and caused the buckling.

Here is a link that might be useful:

Trex is garbage. I have it, love the look of it, but know it's garbage. The buckling often happens, from what I hear, if there is an insufficient gap between boards. The only boards I have buckling are the ones that frame the interior of my koi pond. Overall, I'm not impressed with this product, but it beats pressure-treated wood. I treat the deck as if it were my interior floor and sweep daily, power wash weekly.