It's the clocks on all 24 GPS satellites, all 24 Glonass satellites, and the 8 (so far) Galileo satellites, all going "haywire" by precisely the amount predicte

It's the clocks on all 24 GPS satellites, all 24 Glonass satellites, and the 8 (so far) Galileo satellites, all going "haywire" by precisely the amount predicted by a theory developed before the first satellite went into space. And it's not a paltry amount - if we didn't understand and plan for this amount, the GPS system would have an error drift of 10km (~6 miles) per day