This could be something minor to an absolute catastrophe waiting to happen.
Depending on how the brake upgrade is set up (external hats?) it could be a number of things; stud shoulders not allowing wheel seating, hats, calipers etc. If the rotors were replaced all round then the rear hubs came apart, could be just the half shafts or something far more serious.
Please, please get the car transported straight back to the brake upgrade installer for a thorough inspection and correction.
Julian
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