It must be on Modern. Legacy is for planes converted from FSX. Switch to Modern and apply and save and try. As for reboot… If switching to Modern does not help, you can try this - uninstall the plane, quit from MSFS, clean your *.tmp files from the Windows TEMP folder, clean your C:.…\Microsoft Flight Simulator\cache\0 foler, the C:.…\Microsoft Flight Simulator\DCE\76561198045457618 folder, clean your C:.…\Microsoft Flight Simulator\SceneryIndexes folder (some people clean them every time before a new update), check in C:.…\Microsoft Flight Simulator\Packages\Official any remnants of the plane you uninstalled and delete them if there are any, unplug your controllers from USB, reboot your PC, plug in your controllers, start MSFS, install again your plane, check that the flight model is on Modern and load a flight with your plane and check the plane’s behavior.
If this does not help, ask Microsoft or, may be, anyone here may help.
By the way, they updated the Miss America and the Lady B in the latest beta with their new version of GPS, you can try this beta as well, I just can not guarantee that you can painlessly quit from their betas)