UE Errors

Play VR Mode window is hidden on game start

Unreal Editor errored loading

You have to kill the app OVRServer_x64 via the Task Manager

ComposeRotators()

RotatorAB = UKismetMathLibrary::ComposeRotators( RotatorA, RotatorB));

RotatorBA = UKismetMathLibrary::ComposeRotators( RotatorB, RotatorA));

RotatorAB != RotatorBA !!!

ComposeRotators() has matrix multiplication inside. Matrix multiplication is not commutative.