Air carrier Captain reported GPS malfunction during cruise. The Captain indicated GPS malfunction resolved prior to descent and all GPS systems restored.

Narrative

Prior to this event; we had a GPS failure at cruise that lasted about 275 miles at FL380. We followed all applicable checklists (GPS; TERR POS; RUNWAY SYSTEM; ADS-B OUT L; ADS-B OUT R) and read the aircraft GPS Jamming document in content locker. During the failure; the ANP got up to 3.95 in a RNP 4.0. Using the EFB position dot and track overlay; and radio contact with control; we verified we were just over 3NM South of the track. We contacted dispatch to inquire if other aircraft had reported GPS interference but no other company aircraft were in the area. Control later reported that another type aircraft reported GPS interference at the same location. After enabling radio updating IAW (In Accordance With) the GPS Jamming document; the failure seemed to resolve prior to descent and the ANP returned to around 0.05 with all GPS systems restored and all FMS configuration back to standard. On arrival to HKG; we were given vectors to the initial segment of ILS 07L. ILS 07L is an ILS approach with RNP1 initial and missed approach segments. Our last vector to final was 040 heading; descend to 1500 with clearance for ILS 07L approach. The FAF is VH702 at 1500 feet. FMAs (Flight Mode Annunciators) were Speed; Heading SEL; FLCH with LOC and G/S armed. On initial intercept of final approach course; the aircraft went thru localizer raw data but seemed to follow the magenta line. A few seconds later the aircraft began correcting back to LOC raw data final course and LOC was captured. Simultaneously; the aircraft issued an alert of NAV UNABLE RNP with a RNP 1.0 and an ANP of 1.21. The aircraft looked like it was going to go through the LOC again so I disconnected the auto pilot and began to fly the flight director. We were approximately 5 miles from the runway; on localizer raw data course and about a 1/8 of a dot high on G/S (1600-1700 feet); but the flight director seemed to be giving incorrect steering commands away from the raw data course. The F/O attended to the NAV UNABLE RNP checklist to ensure no limiting factors for final approach (none due to ILS). I abandoned the flight director and few raw data LOC and G/S to maintain the flight path. G/S was captured about 1200-1300 feet. FMAs were Speed; LOC; G/S. The raw data showed aligned on the localizer course and glideslope; but the flight director still seemed to command steering off the raw data course. The F/O acquired the approach light system shortly thereafter and crew acknowledged and visually acquired the runway. BEFORE LANDING checklist was completed. RUNWAY POS alert was displayed. The Relief Pilot informed the crew that no clearance was given and missed approach altitude to be set. The F/O set the missed approach altitude and inquired with the Director and we were given clearance to land 07L below 500 feet and a switch to tower. Due to RUNWAY POS we never received an approaching runway call. We landed without further incident and contacted tower who issued taxi instructions. During the taxi; the ANP never got below 1.21. RUNWAY POS alert and NAV UNABLE RNP alert went away shortly after Captain's shutdown checklist was complete. Cause: Unknown malfunction of GPS and or navigation system.Suggestions: Do not know. Would like more information.