I have created a saving system that makes use of the Save Game flag.
The point of the system is to make it as easy as possible to configure. However, structs created in BP can not be serialized.
When I set the SaveGame flag on a struct variable in BP, it will not get serialized and restored. I suspect it is because the actual members of the struct do not have the SaveGame flag set, as it is not possible to set that flag in the Struct-Editor.
I tested this by creating the same struct it didn’t work with via C++, and set the SaveGame flag there properly with the UPROPERTY specifier.
This could be serialized and restored. So please, Epic, make the Struct-Editor in BP more accessible, as it currently is impossible to easily serialize structs without C++ coding. It makes the user experience much worse.