Hello Michel! Welcome to the forum.
How are you loading the flightplan into MSFS2020? If you’re exporting the file from Navigraph Charts to the simulator using a .pln file, you need to make sure not to change any parameters once the flightplan has been loaded. This includes changing the approach/runway, gate, etc through the planning interface inside the simulator.
The reason for this is that the simulator automatically re-calculates the whole route using its own route calculator upon any changes.
Please advise if you have taken this into account and still experience the issue!
Regards,
Malte