If the initial camber was caused by too low of a ride height, and re setting the TB corrected that, and later after more runs, the camber returned, and if you would be able to once again further torque the TB's to eliminate the negative camber, I would say, the TB's have been over stressed, and now are useless and likely dangerous, and/or you need a slightly larger dia TB replacement for the application or one less fatigued from over stress when replacing. ( king of run on )

Wiki:
"Plastic deformation[edit]
See also: Plasticity (physics)
This type of deformation is irreversible. However, an object in the plastic deformation range will first have undergone elastic deformation, which is reversible, so the object will return part way to its original shape. Soft thermoplastics have a rather large plastic deformation range as do ductile metals such as copper, silver, and gold. Steel does, too, but not cast iron..........

Under tensile stress, plastic deformation is characterized by a strain hardening region and a necking region and finally, fracture (also called rupture). During strain hardening the material becomes stronger through the movement of atomic dislocations. The necking phase is indicated by a reduction in cross-sectional area of the specimen. Necking begins after the ultimate strength is reached. During necking, the material can no longer withstand the maximum stress and the strain in the specimen rapidly increases. Plastic deformation ends with the fracture of the material."