Without looking at your BP and whats actually happening I have to guess. I asume you use “Launch Character” (based on the Tag) and it happens while you are on the Conveyer Belt. The Launch uses Physics Velocity and I guess your Belt constantly applies a Physics Force too to move your Character along. So if you add those two Physics forces together you get both Forces instead of just the Launch Force.
So you have to Set your Velocity to 0 (resets any force that is curently active) than Launch the Character and tell your Conveyer to ignore your Character while he is in Air.
Everything just a guess because I dont know your Game mechanics but that should bring you on the right track to solve the Problem.
Good Luck