Here's my $0.02, and I've seen this occur many times in the race cars and street cars. It's just a theory for a car I don't know (your's) but here goes...

It's possible the rear shocks are dead, with 50k on the vehicle the front and rear dampers would normally be worn out if they're not the electric ones. The standard Sachs/ Boge stuff on all newer cars don't last like they used to and 5yrs or 50k is about all we can expect to get.

If the ride height is at the minimum spec, with new shocks it will bump back up just a bit probably bringing the neg camber into spec.

It's also possible that the rear suspension bushing are spent, even though there may be no visible tears. They can also be compressed and "stuck" on a certain position and worn in. You could and can loose each arm (lower control + camber arms) to let the rubber bushings reset themselves (this happens on Porsche's all the time whether the customer knows it or not) but they'll likely take the same position after a few thousand miles.

Well just some thoughts from things I've seen. Could also be the alignment tool they're using. See if you can find a hand held camber guage with the bubble (ie from Smart Racing's Smart Camber Guage) and do you own test also.

Best of luck.