⟨10kaborl⟩ Hi everyone, I was making a highly elliptical orbit around Earth: Ap 100k km and Pe 200 km aprox.
After that, I set a maneuver in the Flight Planner exactly (~5s error) of when the Ap was predicted to be.
However, after coasting to it then I realised it was off considerably like dozens of minutes.
I understand that orbits change due to orbit fluctuations. However I also understood that Principia's  predicted orbits were accurate (e.g. Ap will be where predicted once I get there).
In contrast, a Moon Pe rendezvous was very accurate to the second when predicting trajectory from Earth. But this highly elliptical orbit wasn't.
Where am I wrong here. Thanks.