I have a 2015 Hyundai Sonata 2.4l gdi with just about 30k miles on it. I’ve recently noticed that every so often after the car has been driven and has been at operating temperature for a while. I’ll go in to the gas station for a drink or something and Then when I start my car it doesn’t really start the way I thought a car should start… so when I go to start it, it kinda sounds like it struggles and it goes to about 600rpm and works up to 800rpm within seconds and idles there. But usually my car always used to start like any other car does and spikes up to 1200rpm then drops because it’s already warm. Any clue as to why it does this? Or is it just normal?
If you’re concerned, I suggest you bring the car to your local Hyundai dealer, before the warranty expires
And save all the paperwork, even if they find everything to be normal
That way, if it won’t start 6 months down the road, when your warranty has expired, there will be a paper trail, proving that you complained BEFORE the warranty had expired
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Good advice from db, as usual. I recommend following it. 
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Concur w/warranty advice above. No, it isn’t normal and needs to be addressed asap. A couple of common things I can guess could cause that. The rail fuel pressure isn’t holding due to failing check valve or leaky fuel injector; or an ignition part is heating up as the engine sits and heat soaks and is starting to fail, like a crank position sensor or ignition coil.