My packaged version of the Puzzle Platform project was failing at startup with the following error:
Assertion failed: Index != INDEX_NONE [File:D:\build++UE5\Sync\Engine\Source\Runtime\Engine\Public\Animation\Attribute Types.h] [Line: 117] Missing operator for attribute, type Integer Animation Attribute was not registered previously
In case anyone else runs into the same issue (using a UE5-created Third Person C++ sample project), you can comment out the code inside the constructor to the automatically generated GameMode class that was generated with the project.
// static ConstructorHelpers::FClassFinder PlayerPawnBPClass(TEXT("/Game/ThirdPerson/Blueprints/BP_ThirdPersonCharacter"));
//if (PlayerPawnBPClass.Class != NULL)
//{
// DefaultPawnClass = PlayerPawnBPClass.Class;
//}
I commented that out and then created a separate blueprint custom GameModeBase which I used instead, and then the packaged version of the game worked.