You must let your class know where to get its Config values from. In your header file add a Config property to your UCLASS(Config = Game) if you’ve saved your config properties in DefaultGame.ini file. Next, in DefaultGame.ini file, you must also explicitly say to what class these values refer to (Or in other words, where your UCLASS should read its variables from). Something similar to following lines should be added to your .ini file (See that the configurable UPROPERTY members are initialized as a Key=Value right beneath the class address).
[/Script/YourProject.YourClassName]
SomeFloatVariable=1.0
Hope this helps.