I doubt it is the maintenance. From reading another thread, these ADIRU's are supposed to remain in situ for long periods of time. They are designed with multiple redundant systems so they can have failures and not need to be removed.
The MAS B777 had some parts of the ADIRU fail a couple of years beforehand, as did the first QF one. Neither meant the unit required replacement.
Why was it the No 1 ADIRU again? Another coincidence?
My money is on a software fault deep in the bowels of the system somewhere.