Welcome to the community @Aiddison.
It does hint in the trainer not to overuse the speed cheat. 
Climbing, using certain things, exiting vehicles, using the teleport cheat, etc will cause Sam to catapult into the air if you have the speed cheat on. The reason this happens is because he is moving too fast, that the game doesn’t know what’s going on. You need to turn the speed cheat off before doing these things.
There’s nothing the trainer developers can do, it’s something that’s related to the game’s coding. Trainers do not alter a game’s code. Turn the cheat off when you don’t need it (ie, when you’re not running on a flat road).
Also, Sam cannot die. He gets sent to the “beach” where he has the opportunity to collect some bonus stuff from other dead players before coming to come back to life. There will also be a crater in the game afterwards where an explosion was triggered in the place of Sam’s “death” which will take a few in-game months to slowly recover back to normal. The game is called “Death Stranding”, as in death is stranded, trapped.