I"m having this issue with the bed leveling, it wasn't the nuts in my case, but the armature that holds the bed. When tightening or loosening the wing nuts, the armature is flexing causing the bed to remain at the same position and making it impossible to level. I haven't fixed this issue myself, I'm currently looking for a fix (other than spending $150 on aluminum replacement arms).
I don't know if any of this will help you, but it's worth checking.