You must Initialize the stream like this to have new seed or it will always use seed zero
FRandomStream Stream(FMath::Rand());
than use it to create random stuff
int
Stream.RandRange(0,999)
float
Stream.FRandRange(0.0f,1.0f)
bool with weight
UKismetMathLibrary::RandomBoolWithWeightFromStream(Weight, Stream)
to re generate the seed use
Stream.GenerateNewSeed()