ATCBob

Exactly. Where they show it "following known waypoints" is at least 80nm from closest shore and probably more than that to the radar source. That's already approaching the edge of even US enroute radar. Unless they have ultra-long range radar (don't know why they'd need it...) they're probably trying to track a giant blip 8 miles wide skipping around as it passes other aircraft above and below it. Computers get confused and you get "track jumps" where it latches onto a different target. That could easily account for that sudden zig-zag "turn" -- the track jumped to a different aircraft that was indeed following "known waypoints." They'd need to correlate the military radar readouts with the civilian readouts, which are all probably plotted on lots of paper. That will take awhile to go through. Hopefully that's what they're doing now.