To be honest it sounds like some material shrinkage.It may be shrinkage in the filler,2k primers,or all the above.This tends to occur in the baking process or when work is rushed.This happens to the best of us.When doing large jobs at this level they should set for a for a few weeks before your final sand.This allows for any off gassing and shrinkage to happen which can be sanded out later.When dealing with many chemicals and human error things happen period.In saying this they should stand behind there work,if not bash away.A shops measure in quality is not just in the job,but in the overall service.This means service before,during,and after the job.
I will respond to a couple of comments about cost and restoration work compaired to insurance work.Restoration work is very time and material consuming.I don't know anyone that works for free by choice.Restoration work also consumes three times the shop area as an average insurance repair.
Time is money,materials cost money,shop space(heat,electric,cleaning),and paint booth up keep/cost.If you have never done a high end restoration or build you will never grasp the amount of time it takes to do a high end build...I am very surprised that any shop touches restoration work anymore do to the high cost of materials.Profit on insurance work has been chopped to a minimum.Profit on resto work was marginal period and is next to nothing now.All the DIY guys take a pen and write down all your time,electric,gas,materials,equipment,space,and add 15%for things forgotten.Now take and put a dollar value next to it,add it up.Now figure the majority of DIY builds are driver quality,so add 100% cost increase on top of it to reach a high end build.People tend to pass judgement based apon ignorance.Look at the facts,time and skill cost money!!!!!!!