For whatever it is worth I had exactly that same situation on a larger tractor/loader, MF2660 and DL250 loader when it was new. After 50 hours or so it seemed like there were loose bolts/nuts all over the place. Specifically the loader mounts were the worst. Wheels were similar but not as bad. Having tightened them down good and solid I have not had them loosen again in over 300 hours. Maybe that is what happens as they settle in. Maybe they were not tightened well to begin with (which is what I think.)
Had the same thing with a JD 4700 back in 2000. It was new then too; mainly wheels loosened up.