problems stomach /carbs after few hours

I'm training and recently finished a few ultra trailruns (100M). After 8 hours everytime I have problems with eating and for the rest of the race it is a horror.
What happens is that I have the feeling that I have to vomit and sometimes I have to vomit but nothing leaves the stomach.
After 8 hours, when I put an energy bar/banana in my mouth, the vomitting reflex starts. The end result is that my energy goes away from lack of carbs in my body until the end of the race.

I already went to a doctor. 2 days previous the race I eat every day about 1000g carbs. With the carboloading I don't have any problems. No vomiting reflex.
During the training I eat about 75 gr every hour, also no problems (I train maximum 8 hours in one day).

I also train with different brands of bars/ drinks to get used to the different types.

Does anyone have experience with this problem or has a solution?

Sounds like classic long-race GI stress, after 8+ hours, the stomach slows down and can’t handle solid food well. Many ultra runners switch to more easily digestible fuels like gels, chews, or diluted drinks late in the race. Small, frequent sips instead of large bites can help.