If I immediately go to the World Map as soon as the home menu appears, when I select a departure location, my FPS drops to 12fps, if I proceed with the flight, the FPS remains sub 20fps.
However, if I wait 10 seconds before going to the World Map (when the sim first loads), or if I exit the world map, and re-enter, the FPS remains normal.
Edit: This may have a bearing on the latest 1.14.5 FPS issue.
I can do this consistently every time I run the sim.
It seems that there is some house keeping going on while the Home Menu first appears, however, if the user immediately goes to the world map and selects a departure, something adversely effects the performance.
So far, I have reproduced this on my AMD 3950x, but not my Intel 4970k. (the 3950x has an older nVidia driver for VR reasons)
Not a biggie, but I have raised a zendesk report in anycase.
Edit: Zendesk have accepted this report forwarded on to the dev team.