Bad camber mysteriously came back

Well about a year ago I had a camber kit put on the front and had the same place do the rears. When I picked up the car it was awesome. All 4 wheels were straight and upright. I drove for 6 months and the tires never wore unevenly. Well I just came back from a 13 hour trip to fla and now im showing thread in my back passenger tire. And there is noticable bad camber. I took off the wheel and the arm and washers are still intact. I had just had my strut replaced hoping that was the problem but its not. Why would my camber revert back negatively over time? can I just add more washers to fix it?

could you have possible bad bushings in the back, that can throw your alignment right out the window.

Good luck