Hewlett:
Never heard about double failure. Sitting in MCC ,we have normally no big issues with ACM's in common. But like You mentioned, cooling air is taken from the turbine inlet of the ACM to bleed the air bearings. It might be, that a long grd time can contaminate them, but like I told you , it is not common. My last time was 12 yrs ago on an A320, double seizure on ACM due to long GRD time before delivery. (long means 6 month) but also here , one by one , with a 2 week timeframe. AB went on warranty without any trouble, when back to work, I will look for a TFU, I remember there was one .
Rgds