I think the problem may be with those tubular control arms.

You could plot the caster, camber and toe change through the suspension's range of motion or replace them with a set of stock ones and see if the problem goes away.

There's not a lot of things to cause this. A balljoint with a tight spot in it or the box itself but you seem to have covered those bases.

You could take it to another alignment shop, don't tell them anything other than you want them to set it up on the machine to check it and see if their results resemble the readout from the shop you are using.

Kevin