Funny that I had a similar issue and after measuring and looking I found the centre bolt that holds the spring pack together had decided it doesn't want to be there anymore and this caused the springs only on one side to slip back only about 1/4" inch but was lucky to find it before something worse could of happened. Also checked the others and all good. Maybe worth a look though.
Alko used to tell us that that bolt was only to hold the spring pack together and wasn't essential, now they peen the thread to stop them coming out ......... go figure ........... the bolt "should" be put in so that it's captive by the axle, so if you undersling reverse the bolt and peen the thread.
when i triangulate a van i put it on stands remove wheels and hub, and drop a plumb bob to the ground from the centre of each axle and the centre of hitch, mark them all on the ground and then measure to the centre of the hitch, also measure between wheels if it's tandem, usually within a few millimetres if all good. and it's usually leftside we see problems with, as this is the working side of van, with potholes and road edges taking their toll on tyres, rotate your tyres as often as you can. the play on the axle pad to the spring bolt is enough to throw it out a bit, so i always push the axles forward or back on the bolt to try and keep them all the same if i've had the u bolts off.
also keep an eye on any suspension play especially broken welds on the head of the bolts, centre bolt on tandem is important as if that bolt comes loose and wears the hanger a new hanger will be needed to be welded to chassis, seen it so many times it's not funny and costly as well. easy to check by jacking one side and using a pry bar to see if there is any play
