Hyundai i30 reverse gear not engaged

I have 2015 hyundai i30 1.6 crdi dual clutch transmission car, sometimes the reverse gear could not engaged until i turned off the car and restart it, after a while and when the car was on and steady, i noticed that the check engine light is on, and when i drove i noticed that the second gear could not engaged (1st to 3rd gear directly) until i turned off the car and restart it but the check engine light was still on, and after one or two hours i turned off the car for about an hour, and when i restarted it the check engine light just disappeared by itself and the car was normal after that, and i went for a long trip without any problems, note that when i did a computer check for the car, the only error in history was "the reverse gear R could not engaged".
So please if you can diagnose the problem for me and thank you.