I am a long-time X-plane user too. You are correct, these USR points are not standard and not a part of IRL flight plans. They are a kludge introduced by the bad AP system that MSFS uses. You know how the Toliss or FlightFactor Airbus will sometimes follow a curved flight path if that is the published route? MSFS doesn’t have that ability so they “force” it with these kludgy waypoints. Unfortunately that means that you sometimes get that wierd issue if you miss one.
That’s not just my interpretation; many people have figured this out. But you do have to carefully watch the AP in MSFS. It’s kind of like how the JarDesign Airbus was. Generally ok but prone to sudden, suicidal behavior.
I wasn’t trying to come across as aggressive. I just don’t like seeing bad advice being propagated. That just creates further problems for people down the road. Sorry about that.
I’m really looking forward to the FlyByWire custom autopilot which will do away with these USR points and make the plane fly correctly.