I may have found a solution. I had the exact same problem. Whenever i opened UE4 i got the error :-
“Default property warning and errors: Error: CDO Constructor (SurviveGameMode): Failed to find /game/ThirdPersonCPP/Blueprints/ThirdPersonCharacter.ThirdPersonCharacter_C”
Before i started getting this error i had moved the ThirdPersonCharacter blueprint out of the ‘ThirdPersonCPP’ folder to another folder i had just created.
To fix the error i opened TP_ThirdPersonGameMode.cpp and edited the following line in the contructor. :-
static ConstructorHelpers::FClassFinder PlayerPawnBPClass(TEXT("/Game/YOURNEWFOLDERNAMEHERE/ThirdPersonCharacter"));