If it’s NEI of itself, then it’s always looking at its own previous conditional trigger evaluation. The first time it hits one (beat 2) there is no previous conditional trigger so it’s false and on an NEI trig, so there’s no trigger. The next time it hits one (beat 4) it’s looking at the previous trigger from beat 2, which was false - but it’s an /NEI so it’s a trigger. Then the next bar those would be reversed because the next Beat 2 NEI would be looking at the previous bar’s beat 4 which was true, so it is also true. and so on…
The manual doesn’t say track 1’s neighbor is itself, but I’m just thinking it must be because of that behavior… if it was just looking at a ‘blank’ nonexistent neighbor track, then it would be 1,3,4 every time.