Leash breaks because of car storage?

I just had a long swim after my leash broke. The material that connects to the ankle strap broke, the elastic band is fine.
It was a nearly unused 8ft FCS leash, I bought it for my 7'9" malibu for bigger surf. But since I moved to shortboards 2 years ago I hardly ever used it, and left it in the back of my car (hatchback) for backup. Until today when I took it out with my 7'4" semi gun for a 6ft swell at Batu Bolong.
I gave it a good stress test before I used it, everything seemed fine, but I guess a 6ft wave pulls alot harder then me.. It is a bit scary that a leash that looks perfectly ok can break this easy.
Could it have been because of heat in the back of the car storage that weakened the plastics?
It was a nearly unused 8ft FCS leash, I bought it for my 7'9" malibu for bigger surf. But since I moved to shortboards 2 years ago I hardly ever used it, and left it in the back of my car (hatchback) for backup. Until today when I took it out with my 7'4" semi gun for a 6ft swell at Batu Bolong.
I gave it a good stress test before I used it, everything seemed fine, but I guess a 6ft wave pulls alot harder then me.. It is a bit scary that a leash that looks perfectly ok can break this easy.
Could it have been because of heat in the back of the car storage that weakened the plastics?