Wheel studs spin/wobble in practically new wheel hub assemblies

Had a problem I have never had before in all my years of tire changing. Got new tires changed out at a shop the other day and had several studs just loose and wobbly. But let me back up a bit. All the loose studs were in the front wheel hubs. One of the hubs (which come with the studs pre-installed) was replaced within the past 6 months with an "affordable" brand, and the other under year prior to that with a nice Timken brand. Did the repairs myself and had no major issues with either job. The newer hub had three of the five studs just spinning loose when they tried to put the new tire on. They were able to use a tool that pulled the studs back in tight and that worked for two of them but the last stud would not tighten and now I am currently driving with 4 lugs on that side, The slightly older but still pretty new Timken had one loose stud that would not snug back into the hole and so that side is also with only 4 lugs on. We didn't take the brakes/rotor off so I did not get a good look at what the problem really was but I assume that either the hole or the ridges on the stud are stripped/worn out. Why would this happen to fairly new parts? I am guessing the answer is going to have something to do with the tire being reinstalled using an air gun. I know this is not the best way but I can honestly say I have never seen any shop put a tire on any other way and I have never had this problem before. I need to take a look and deal with this but I am fairly certain that I may not get a tire back on, and that is if I can even get it off. Does anyone have any insight into which part is most likely destroyed, the studs or the hub into which they are pressed? I can't believe I might have to buy another $200 worth of wheel hubs that were just replaced! Honestly I bought the cheaper wheel hub assembly thinking it should still outlast my 2005, 215,000+ miles Prius and perhaps that was a mistake, but the Timken? I bought that one due to suggestions here at Priuschat. What do I do?

 

I've never sought professional assistance (if you mean taking it to a shop) and I never will. I just thought someone here may have an idea which the weaker metal was. I'm betting on the hub, unfortunately.

 

The threads are fine. The studs are not staying in place in the hub. However, I do assume that over tightening with the impact wrench has been the cause.

 

Can't say what is really happening till I take a look I guess. The studs came pre-installed on the wheel bearing hub assembly.

 

Tire shops I have gone to have always used them and I never had the problem before either. I bought both hub assemblies from rockauto.com. I won't be able to take a look for a while. No days off work for two weeks.