It's usually not a factory defect, but more of a technique thing. The deal is that air fryers, even Philips ones, have zones that are a bit less hot - often toward the corners or the back. If you overload the basket, the hot air doesn't circulate properly and you're definitely going to get uneven cooking.
What I'd suggest: start by putting less food in at once, seriously less than you think you can fit. And most importantly, shake or flip your food halfway through cooking - it's not optional, it's the key. For fries for example, I pull the basket out at the halfway point and mix it really well. For chicken or stuff you can't shake easily, I flip it a quarter turn. It makes a huge difference. If even with that you still get some spots that are really undercooked while others are burnt, then maybe there's an actual heating element issue going on, but honestly I'm betting you'll see a big difference just by reducing the amount and stirring things around.