A large commercial turboprop plane is shown taking off which then transitions to its interior, showing FBI agent Harris concluding CIA Station Chief Wright that Ryan is in Semmering, Austria. However, when they land, the jet landing is a smaller, private corporate turbojet plane.
Trains in Austria have two red taillights and not one.
The opening of the door on the train as shown would not be possible since the opening mechanism is deactivated while the train is driving (it could be opened via the emergency handle but that would result in an alarm).
During an overhead shot of the train from Vienna to Budapest, you can hear the horn of that train. However, the sound effect used is from an American train.
Sarhan's rifle has no scope, but when the camera looks over his rifle from his point of view, the camera shows cross hairs from a scope.
When Greer & Kovac are discussing Russia's plans to move troops, Greer mispronounces Slovakian as souvlakian. "All the way to the souvlakian border."
A scene with a landing plane is titled "Semmering, Austria".
There is no Semmering Airport. (Semmering is located in a mountainous skiing area.)
The train arriving in Semmering approaches the station from the wrong direction on the northbound track towards Vienna, although it departed from Vienna.
Around minute 19, while Jack Ryan is talking to Greer on the phone, in a short shot Ryan is holding the smartphone upside-down.