I found out why this is not working, I was using the wrong formatting value. My CurrentScore variable is a float so I should have been using %f in the Text. %d is used for integers so if I change the line of code from
UE_LOG(LogTemp, Warning, TEXT("Current Score: %d"), GetScore());
to
UE_LOG(LogTemp, Warning, TEXT("Current Score: %f"), GetScore());
The Output Log displays the correct value, more information can be found on the Unreal Wiki below: