I don’t think flight plan upload or flight plan updates from the Garmin is enabled. I’m not sure why you are saving the flight and then (immediately?) loading it again.
The use of a flight file *.flt is not well documented or supported. In addition, each .flt file is customized by the aircraft choice.
It is logical to think that saving and loading a flight file .flt should work any time and and any where. But unfortunately that isn’t how flight files work. The ONLY time they work correctly is when a restart is done at the end of a flight. This is because there are three different sections of the .flt file that contain flight plan information. One of the sections contains a pointer to a flight plan file .pln which is incorrect. When you try re-using a .flt file, the flight plan is not displayed BUT the flight plan information is in the NAVLOG top menu item and may or may not be displayed on the VFR Map.
Where are you creating and then attempting to save a flight plan? On the World Map?
An active flight plan is not a .flt file. As I mentioned the .flt file contains an incorrect pointer to the .pln file.
Even though many tickets have been submitted through ZenDesk, Asobo seems to be reluctant to fix this issue. It is sort of working as it was initially designed.