Air carrier captain reported during the initial approach a late change to the STAR arrival; runway change; a problem loading the FMS with the new STAR and continual GPS jamming in LTBB airspace. The captain states these events caused a track deviation.

Narrative

We were filed and planned for the ATPIX 2N RNAV arrival. Planned for runway 35L; but briefed the ILS 34L as advertised on ATIS. Approximately 2 minutes prior to ATPIX were cleared via the ATPIX 2A got runway 34L. And given a descent. FO attempted to read back [but] his headset would not transmit. While he was busy with that; I changed the arrival to the ATPIX 2A. It loaded on page 5 of the legs after a discontinuity. I selected ATPIX from page 5 to the scratchpad and moved it to the active (1L) of page 1 and executed. It immediately returned to the original ATPIX 2N followed by a discontinuity and then the ATPIX 2A. I attempted again to verify I had actually moved ATPIX to the top of page 1. Same result. A final attempt was successful; but only (I think) because it occurred exactly as we were sequencing the ATPIX waypoint. This caused the aircraft to begin a right turn to go back to ATPIX; instead of the appropriate left turn to the next arrival fix. After a several second delay; I realized what it was attempting and changed to heading mode and a left turn to rejoin our course. Because of our altitude and speed this was a slow; shallow banking turn. We ended up being approximately 6 miles north of the magenta track before we were headed in the correct direction. In the meantime; the VNAV had stopped descending and was just hanging out in VNAV PATH; even though the VDI showed we were 1000 feet above path. ATC cleared us direct to the next point and gave us a further descent and said expedite for traffic. At this point I selected Vertical Speed and rolled into a 3000fpm descent. After this point; lateral navigation worked normally but we could never get the aircraft to follow the VDI path in VNAV and were forced to use vertical speed to meet crossing restrictions. We also received unable RNP (GPS jamming had been actively occurring) but that should not have effected the vertical modes. The FO has more experience on the aircraft and none of us had seen anything like this before. No issue reported to us by ATC.Cause: Unknown. I should have reviewed all possible ATPIX arrivals. I would have seen that the initial 5 fixes after ATPIX were identical and I would not have been 'rushed' by the late assignment of the ATPIX 2A.Suggestions: Be more proactive.