Vehicle stops at certain speed

Hello Everyone. I have noticed that my vehicle slows down once it reaches a certain speed, and I won’t be able to control it again. Usually, it doesn’t slow down but for some reason, once it reaches 24 km/h the speed suddenly drops down, and no matter how long I press “W” my vehicle won’t move. Steering works without any problem. I don’t know what is causing this. Any suggestions?

does it have a max speed set? what is your set-up? how do you “accelerate”? screen shots?