Using UE 4.23.1 and building for Oculus Rift S, if I run the game in editor it is smooth. If I run the build, the image on the computer screen is smooth but in the headset it is laggy.
However if I alt-tab out or bring a different window to focus other than the game window, the frame rate is normal in the headset again.
Wondering if this is a bug or something i’m missing here?
Usually it is exactly the opposite. VR will lag when the VR preview is not in focus. Make sure your video drivers are up to date.
Also you may want to use the Oculus Debug tool to check your performance directly in the HMD. Maybe you spot something which gives you an hint about what could be wrong. The Oculus Debug tool can be found in your Oculus installation folder under Support.