Checking Work With SteamVR
SteamVR will not work with any of the UE4 Editor viewports or the default Play In Editor (PIE) session. To view your project with SteamVR, you will need to use the VR Preview option. To access the VR Preview option, you will need to do the following inside the UE4 Editor:
On the main Toolbar in the Play section, click on the small white triangle that is next to the Play button.
From the drop-down menu, select the VR Preview option and then put your Rift on to view your project in VR.
Once you have changed the play mode to the VR Preview option, your project will always launch in VR, even when using shortcuts like ALT + P.