Editor waiting ~300ms to present

In the last 24 hours we’ve had a sudden performance drop one machine in the team. That machine has gone from running normally to running at around 3fps in the UE editor (4.15.2). The machine has a i7 6700, 16gb ram and an NVidia 1080 card. Graphics drivers were just updated to 382.05 yesterday, so we tried cleaning them off and installed an older driver with no change. We have verified the UE 4.15.2 installation. Trying the Infiltrator demo under 4.12.5, that runs perfectly. I grabbed a profile from a very simple test level using “stat startfile”.

The rendering time is ~5.7ms which is normal for the scene in the editor, but then there is a 324ms wait to present. GPU-Z shows the gpu barely loaded - again comparing with the Infiltrator demo, that clocked the gpu up perfectly and showed normal gpu load.

Day to day this machine is being used for Oculus VR dev, but we unplugging the Rift just in case with no difference. Yesterday it was perfect. Today it is unusable, but we haven’t been able to figure out why. I’ve attached the profile data as well.[link text][2]

Any thoughts as to what is causing this?

Deleting the config directory on the problem machine cured the problem. Unfortunately we don’t know what config setting change had been made to cause the problem, but for anyone else hitting similar problems, check the config.