Many 787s world-wide were affected by this issue, despite Boeing / Honeywell saying beforehand there should not be a problem.
It caused multiple issues & the fix was not straightforward.

Some details would be interesting, if you have any:
Was the fault with the date only, or the actual GPS function?
Is the GPS date used by the aircraft flight systems?
Does the aircraft flight system closely couple to the GPS, or is it read-only?
Do the problems extend to the inflight entertainment, and was that part of the grounding?
What was the difference between B787s that were grounded, and those that were not?