Air carrier First Officer reported experiencing GPS interference after passing EGOBA but the GPS fully recovered after passing KALIG about an hour later.

Narrative

After passing EGOBA on Airway Y697 from ICN to ZZZ; we experienced degradation of GPS signal and had EICAS message: ADS-B OUT. After following guidance for suspected GPS interference enroute to USA; we continue to monitor. Then just after passing position ADNAP at approximately XA:00 at FL330 on Airway OTR5 we had EICAS message UNABLE NAV RNP indication that our ANP had exceeded the RNP alerting reference. We completed the checklist and contacted Dispatch; Maintenance Control; and the Chief Pilot to confer about Electronic Checklist and any other considerations possible. Also confirmed that we were in RNP-10 airspace and no alerting requirement existed. The Chief Pilot did not recommend any need to notify ATC and we concurred. Our position was verified on course/airway with another aircraft. At XB:00 and 80 miles past KALIG direct to CUTEE; our ship's GPS fully recovered and GPS updating was re-established in accordance with the procedures. Our position was never compromised as far as we could tell. Remainder of flight continued normally without incident.