Orignal expressions
FQuat RotationQuat;
RotationQuat.W = CR*CP*CY + SR*SP*SY;
RotationQuat.X = CR*SP*SY - SR*CP*CY;
RotationQuat.Y = -CR*SP*CY - SR*CP*SY;
RotationQuat.Z = CR*CP*SY - SR*SP*CY;
It is clearly that X, Y’s signs have been fliped.
The conversion from Quaterion to Euler Angle is the same. X, Y components in Quaterinon have been fliped, too according to orignal expressions.