This may be hard to reproduce, but I've noticed 2 incidences where my Pristine Black Cargos go from Pristine to Ruined. When I am running around a zombie to avoid it, sometimes the zombie arm hits the clip box even though it's not swinging.
I've notice other items go from Pristine to Ruined in 1-2 hits, like the Motorcycle helmet.
Not entirely sure how to reproduce this accurately. I would assume, get gear head to toe (helmet/hat, vest, shirt, pants, boots) and run around zombies when they are agrooed. When you try to run around them, they won't be swinging but you will get hit. In my case, ruins a pristine item.
This has been reported before and the devs have said it is a random event. For a random event it happens so often I have lost count of the number of times I have lost items from pristine to ruined by 1-2 Hits from a zed. Because of this I run around with ruined Clothing and nothing of importance in them. I hope they sort this out soon.