Loose Gas Cap

This is the second time I had to take my car in to get her checked. Her engine light went on so I took her into the dealership (since I'm still under warranty). They told me it's a loose cap and when I close the cap I should do three clicks to avoid this problem. But I normally do that. I hope it's not something more serious.

My other Prius 2013 never had this problem. I was wondering if anyone else had this problem.