Defective car seat????

So I buckled in my 10 weeks old to his chicco next fit (used with prior child) and went out to pick up his sister from preschool. I put the winter cover on and when pulled down the top so his face was exposed. Then when we got home I saw that the chest buckle was COMPLETELY unbuckled 😱😱😱😱 I almost had a heart attack. I am so thankful to God that nothing happened. But now I’m thinking we need a new car seat. But I’m also not sure if maybe I accidentally pulled some of his onesie into and it didn’t shut all the way 🤦🏽‍♀️ I keep replaying it in my head and I just hold him tighter. I am triple checking all buckles from now on!