Most likely it's a fuel
Most likely it's a fuel delivery or transmission issue. Watch your tachometer. Does it waver? It's more likely to be either a confused CVT (it happens) or the aforementioned fuel issue. If it's the VVT, then it's because you're right at the RPM point where the ECU tells the cam gear to open, but normally you will not know it's happening at all and today's engines usually do so dynamically, so it's not sudden, but gradual.