B757 Undifferentiated or Other Model
Human-Machine Interface; Confusion
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Aircraft; Human Factors
When we passed RESNO entering NAT E at coast out; the flying pilot selected R1 to enter a one mile slop for the track.  The aircraft was in LNAV and we noticed the aircraft flying through the one mile offset track and not turning to intercept it.  The flying pilot selected heading select at this time to roll out; so as not to get off course. This was when we noticed that the next point on our map display; N56000 W02000; was still white and had not turned magenta when we passed RESNO.  Even though the 20 West point was on our map; with the route line leading to it; it had dropped off the legs page.  We re-installed N56000 W02000 on the legs page; so we could re-engage LNAV. As we were doing this we got a SELCAL that our RESNO CPDLC report which was sent when we passed RESNO reported that N57000 W03000 was our next waypoint; instead of the 20 West point.  We confirmed that we were going to N56000 W02000.  All route confirmations and checks; distance and courses; were done correctly before entering the track. The 20 West point was on the legs page correctly when we checked it before passing RESNO; and it was on the map display the whole time.
[Report narrative contained no additional information.]
B757 flight crew reports the aircraft not tracking the desired course to the next waypoint on NAT E and heading is adjusted manually. While visible on the ND the next waypoint is not on the legs page and is not reported as the next waypoint to Shanwick via CPDLC. The missing waypoint is reentered and the crossing continued without further difficulties.