This seems to be a problem of design and there are a few things that could cause a problem of this kind. A: Is the vehicle properly aligned. If the center of mass is not evenly distributed there will be at least one tire with additional pressure on it wanting it to swerve to a particular direction. B: Are the wheels properly aligned. If the wheels are tilted, this is called camber and toe, then the performance will change. If you don't know what you're doing, usually for the worse.
C: Are there any components that are being dragged. This additional contact point on the ground could cause the vehicle to want to tilt, pivot, or rotate depending on its' position relative to the wheels. D: Is there any part clipping that is causing the wheels or parts the wheels attach to, to become unstable E: Is the wheel base that has drive, symmetric. For instance if your vehicle is front wheeled drive and you accidentally also left the back left wheel motor enabled the vehicle will gain speed on its' left side faster thus wanting it to turn to the right. The powered wheels on the right side will resist this and might in particularly bad designed to have the vehicle rock back and forth till it flips. F: Going of the same line; Is the steering enabled properly and symmetrically. Generally when steering is enabled on all 4 wheels even when correctly can still cause issues in rocking the vehicle. G: Is the weight of the vehicle appropriate for the wheels being used. Having too much weight on a suspension of a wheel will break it, but not having enough will cause the vehicle to roll easier. Also this one hopefully never needs to apply to you but is good to keep in mind nonetheless. Keep your center of mass low. If you imagine the line from your center of mass to the contact point the wheel makes with the ground the more vertical that axis is, the easier the rover will be to topple. When you place the vehicle on an incline such that that axis is vertical or more relative to the force of gravity, Then you are beyond the point of return and the vehicle will tip unless you have sufficient torque to keep it upright.