Do you have the same issue if you follow the OP’s steps to reproduce it?
YES
Provide extra information to complete the original description of the issue:
Because, these days, I’m mainly use MSFS for development, my default startup is windowed to the contrary of majority of users. Since the problem occured for those who start by default full screen, my MSFS starts now with a windowed, but in an oversized format (at the last windows position saved)