Potential BP workaround: Get Game User Settings -> Set Fullscreen Mode (Enum: Fullscreen) Then connect Return Value from Game User Settings to an Apply Settings node
Packaged projects will not match monitor resolution when SteamVR is being used.
STEAMVR 1.7.15 used
Result: Game window will extend past monitor boundaries.
Workaround: Unplug HMD or Disable SteamVR plugin and package
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-81377 in the post.