Loading a saved flight via Simconnect is not working

I have a external Simconnect Client app that uses
simconnect.FlightSave and simconnect.FlightLoad

These API works fine in MSFS2020.

In MSFS2024 both APIs seems to work, but…
When a simconnect.FlightLoad is sent MSFS2024 first sets the airplane to the correct location and altitude etc. in the UI window
but then sets the airplane to start at the ground not in the air. Clicking the READY to FLY sets the airplane back to the initial location and altitude.

See [https://www.youtube.com/watch?v=MT2Nl3Th1iQ] for more info.

There seems to me that MSFS2024 mixes up the .flt files in a strange way.

I am in the Free Flight mode of MSFS2024.