Different Versions of Nike Frees

I think I must have picked up a bad pair. I purchased the 7s about a month ago and the first time i ran in them I lost a tread piece off the sole of the shoe. Other than that I love them, way more comfortable than anything else I’ve worn. Oh and for anyone thinking of purchasing I found that I couldn’t buy the one’s with the strap because I have a wide foot. So for sizing that’s something to keep in mind.