"Firstly, the rear wing support section was missing four bolts compared to the homologated version of the car, which Ferrari acknowledged was not compliant with the rules.
...
"Ferrari argued that “the excessive deflection was linked to the missing bolts” and insisted there had been “no performance gain”, but stewards noted the #50 Ferrari achieved its highest top speed on lap 380 out of 387 – implying there was a performance gain thanks to reduced drag.
"A Ferrari mechanic reportedly noticed the absence of a bolt at 3:23pm, less than an hour before the end of the race, but the AF Corse-run squad did not take corrective action.
I've also read that all cars were checked for this (don't have a source for this though), and also considering the nature of this failure, neither the 51 nor the 83 should be affected.