Fountain Tire, Lacombe, AB

I've been coming up to the Fountain Tire Lacombe for great service. It is just today, October 26, 2020 that I have my all-season tires for Honda Odyssey 2007 to replace with the winter tires. Unfortunately, one of my wheel lug nut is missing. I went back to the service center to enquire about it but I was told that the wheel lug nut is missing that's why they've used the spare nut instead. I regretted that I did not check the wheels before leaving the service center. In my opinion it's very unlikely that the wheel lug nut would come out by itself because it needs a key nut to untighten it. I've a question in my mind whether the wheel lug nut came out of itself or somebody lost it or keeping it.