VR game hangs in editor and exe

Often, and very randomly, my VR game hangs and I go to the “This is Real” screen in VR. UE4 stops responding and Im forced to kill the application through the Task Manager. What is the reason for this to happen? I am unable to find any pattern to the freezing/hanging. Could someone suggest a solution? Is this a known issue with 4.12 and SteamVR. 4.11 didnt have this issue.

It has stopped happening once we upgraded to 4.13 and stripped down our map.