car starting

Have a 2016 Mustang GT that just hit 40k miles. Lately I noticed the warmer it is outside It's struggling to start. It happens often but not every time. I am noticing it getting worse though over the last couple weeks. Turns over for up to 3 seconds. Car seems to drive just fine. Any ideas...

So when I went to put my car into accessory mode today, the car fully started without my foot being applied onto the brake pedal. I let it idle for a little then turned the car back off. I noticed after I turned the car off that the green light on the “start/stop” ignition button was fully lit...