I'm having this exact same problem which is why I'm here today looking for it to see if others are having it. Only noticed recently with cold weather. Come to a complete stop at a light, wait a little bit, then push gently on accelerator and this big jerk that scares the s*** out of me. It's such a large jerk it's similar to being rear-ended or something. It's like an engine or transmission seize. I have a 2020 Niro for less than 1 year now. I live in Concord, CA, which is flat terrain, no hills. Same as original poster, it doesn't happen 100%, so it would be difficult to reproduce for the dealership.