This exact same thing happened to me two mornings in a row on my 2021 Seltos Ex Premium. I went to remote start the vehicle, and it didn’t start. I then went outside to the vehicle, and got in and tried to start it. It started fine, but shutoff almost immediately. I tried several times in a row.
I wasn’t sure if the battery was low, so I put a battery charger on it for awhile, and sure enough it started and stayed running after that.
The next morning, it did it again. Again, I tried several times in a row to start it, and it would start, and immediately shut off. Again, I put it on the battery charger, and a couple hours later, it started and stayed running. I drove It straight to the dealership, and they did a battery/alternate/system test on it, and found nothing. I left it overnight with them, to try and start it in the morning, hoping it happen for them the next morning. Of course it didn’t. I went and picked the vehicle up again, and it hasn’t happened to me since.
I’ve ruled out the key fob, as it wouldn’t stay running when trying to start with Kia Connect app, with the remote start, or starting it from inside the vehicle with the button.
I thought maybe it was bad gas, so I filled up with fresh fuel from a different station. And as I mentioned, it hasn’t happened to me since, but like you said, it makes me nervous that it may happen again.
This happened to me on Nov 9, and again on Nov 10.
Please keep me updated if this happens to you again!