Most every car that does this has toe change in and out. It’s not bump steer, it’s flex. Think about what’s happening as the front suspension drops during body rise. The control arms pivot down. This causes the front track width to narrow. You can measure it yourself with a tape measure. When the tires return to the ground they scrub as the track width returns to the original dimension. The rubber bushings flex. The idler arm pivot flexes. The steering box mount flexes. When this happens the distance between the outer tie rods changes. Loosen your idler arm pivot and move it up and down. Watch the toe. The more travel the suspension has, the greater the change in track width dimension. This is why limiting travel helps. Also stiffening the compression of the front shock helps. It slows the process of track change. Watch a rack and pinion car. They are far less likely to have this condition as the steering linkage is mounted very close to the chassis. Not cantilevered 7”-8” away from the mounting points. I have two friends with different style Camaro’s. A 69 and a 79. One has linkage in front of the spindle, one behind. Both have resorted to mounting steering stabilizers on the drag link to slow the process.
Doug